99 996 cold start knocking, rattling

I finally removed the belt to see if the noise was internal, and it is. Here�s a video: You Tube I have to remove the 15w-50 and go back to 0-40, I know. If I just drive off, my car doesn�t really make this noise. It�s only when cold and if I let it idle after a cold start. The noise only happens after 10-15 seconds (it�s not there from 0-10 seconds of the cold start), and it�s not there when the engine is fully warmed up. Sometimes it sounds like a rattle, sometimes it sounds like piston slap, sometimes chains, sometimes valves... What the heck is it?

Why does it sound to be idling so high? Otherwise.....oof doesnt sound good

Check the cats. If that's not it, agree it doesn't sound good.

It does sound good. My car had a similar sound when it went caput. In my case it was a lot more audible and constant, but it would go away and come back. The previous owner of my car ran a thicker oil than recommended. Tisk tisk Are you planning on moving on or rebuilding? You could sell it as a roller and come out with 6-8k. I think someone recently posted they wanted a cabrio roller. Best of luck

It sound like a stuck or sticking valve. I have a 2001 and the manual suggests 10w30 for my conditions. I tried the 0w40 but the engine got a little louder at start up. So, I went back to Mobil one euro 10w30.

That�s one of the rare diesels they produced. That motor is phukd time for a rebuild.

It�s idling high because it�s a cold start. What�s strange to me is that most people report rattling and cold start noise for the initial start (0-5 seconds), but mine is silent from 0-10 seconds. Secondly, if I drive off immediately, and keep the revs above 1500, it goes away. And when the engine is fully warmed up at 180F, no noise at all.

Quotes source post: 14551809

I assume with a stethoscope? Or put a set of good, known cats in place?

You can go into the cylinders through the spark plug holes with a borescope, if cylinders are ok could be a lifter or a valve seat maybe ?

Quotes source post: 14552861

Yes, with a mechanics stethoscope or use a long screwdriver between the cat and your ear (touching both). You can also use the stethoscope to poke around and isolate the source area of the noise better.

sounds like mine did....just not as bad. Scored cylinders. get your cylinders scoped, stop wasting time with other stuff.

Not wishing to be the harbinger of doom, but mine sounded like a lifter, but was the thrust bearing giving up, the engine architecture throws sound in lots of places. Could be dreaded bore score, could be loose plug, could be cats. I have everything crossed for you that it's something really easy. How is the filter, have you checked for metallic particles? Good luck.

Quotes source post: 14553054

Thanks. The filter has been so clean that it�s bizarre. There�s just nothing in there.

https://www.youtube.com/watch?time_continue=10&v=pho496vYxVA https://www.youtube.com/watch?time_continue=17&v=G4wWhD93brE Here is what mine sounded like.

Here is mine. Cyl 4 & 6 were completely done. https://youtu.be/YSRTKH89MdM

gnarbowski: Did they ever pull the engine apart? Or is it still on the waiting list to get started?

Quotes source post: 14555354

I'm still waiting for them to pull the engine apart. I haven't spoken with FSI about when this is going to happen, but I would imagine it would be within the next month or so. I'll be updating my thread when this process starts to get rolling again. Hurricane Irma threw a wrench in the schedule at FSI. They didn't have power or a stable internet for around a week. Some of their vendors were hit even harder, they are running behind. All in all things could have ended up being much worse.

Quotes source post: 14555800

One might wonder if there are any extra m96 engines available due to the hurricanes and flooding that will show up on the market. Not sure how many of them would be �fine�

Changed the oil back to 0-40, so it�s quite fresh now (the old oil had about 180 track miles and about 1,000 Street miles on it, about 3 months old). Still the same noises. Oil filter had nothing, and the magnetic drain plug had a small amount of magnetic silver oil, but no shavings.

Have you checked the cats?

Ahsai, my car makes a similar noise, but for less time as compared to murphy's video...he actually lives about 2 miles from me! Today was a cold day, about 50F or cooler over night, it seems like the colder it is, the longer the noise is around. I used a stethoscope to listen to the engine today.....and the cats, but could not hear anything through the stethoscope. It didn't make the noise until about 60 seconds into the cold start and then not very loud at all, and then went away after 60 seconds or less. Normally I just pull out of the garage, don't let it idle, drive it a block or even half a block under very low power, and when I come to the next stop, it's gone until the next cold start, i.e. it has to sit over night to make the noise. After listening to the engine on the bottom of the cylinders and hearing nothing with the stethoscope and nothing at the cats....I'm going to say I will sleep better, at least tonight. Will change the oil soon again and send it out for analysis, this will be my forth data point on the engine. So far it has a clean bill of health. I can tell you that my right exhaust tips get slightly more soot on the them as compared to the left ones and the engine noise comes from the left side. So that's why I don't sleep so well at night sometimes.

Quotes source post: 14562305

Maybe Murphy can borrow your stethoscope Your description sounds a lot less severe than Murphy's.

Quotes source post: 14562157

That�s high on my list, but I wanted to get the oil done first.

good luck Murphy - hopefully it's the cast!

Quotes source post: 14563539

It does make quite a racket upon deceleration with my Gundo hack. So maybe it is exhaust.

Quotes source post: 14562157

I'm starting to think this is what's causing the noise. Whenever I decelerate (throttle plate closed completely), the racket that ensues sounds like a bunch of marbles in tin can. Separate topic, I finally got around to taking close up pictures of some small, tan, rubbery bits I found in the oil filter. They are all brown and feel like rubber bands except one small black piece (hard black plastic). The largest one is about about 2-2.5mm tall, for reference. I've heard those are likely sealant used. I used to not see anything in the filter, but this particular filter had 2 tack events on it, around 250 track miles and 1300 miles total on the fresh oil. I was shifting up at 7k and pushing the car pretty hard, so I'm not sure this car has ever had that much potential G-force and oil windage ever in it's 18-yr history before.

1999 996 C2 (0.5-2.0mm in size) small brown rubber bits in oil filter after 250 intense track miles, 1300 miles total on fresh 5-50 full syn oil

Quotes source post: 14659345

The soft bits are sealant. Not factory sealant either. I believe all sealant used is black. The hard bit is probably a piece of plastic off of one the chain guide rails. I think the crankshaft to IMS chain drive uses black composite plastic. Not uncommon for a bit of plastic to show up in a tracked car. Have the camshaft covers been off? I'm thinking if so perhaps the wrong sealant was used. The sealant between the camshaft cover and head doesn't form a thin layer but instead gets flattened out so the camshaft cover and head fit together "metal to metal". (The sealant does fill the small voids that exist between the camshaft cover and head these voids being the result of the machined surface finish.) If the wrong sealant was used the camshaft cover may not be metal to metal against the head at all places. If the camshaft cover doesn't fit metal to metal this results in excessive camshaft bearing clearance which can divert oil from the lifter bore supply and a portion of the valve train doesn't receive the proper volume of oil at the proper pressure. The result can be a noisy lifter. It is imperative the camshaft cover fit metal to metal on the head. The camsahft bearing bores are machined with the camshaft and head bolted together metal to metal and the only way to ensure the bearing clearances are correct is to bolt the cover and head together with 100% metal to metal contact. Or if the sealant ended up as a thin layer (at least in spots) between the cover and head a section could have been forced out (by oil pressure) from between the camshaft cover and head. In this case this is a high pressure internal oil leak. Again the result is a part of the valve train gets a sub-par supply of oil and extra noise can be the result.

Quotes source post: 14551680

Hey I have the same noise on my 99. Did you find out what it was?

I had a rattle that only happened when cold and on deceleration turned out to be loose baffles in the mufflers had a welder cut them open and tack weld the baffles back and the rattle went away

Quotes source post: 15395785

Nope. Still does it. It sounds like a can of marbels. Just today in a parking garage, on deceleration, same marbel sound. So it might be exhaust...

So it hasn�t got any worse? Mine is the exact same sound. It�s unrhythmic like a rattle. I saw a video on YouTube which is the exact same noise and the poster was German. I managed to translate one of the detailed responses from the comments are and this commenter Said it is caused by the piston from the Oil pressure relief valve. It only happens very early cars and is the piston rattling around in the casing. When the piston warms up expands a bit and doesn�t rattle slightly so you can�t hear it quite so much. There was a replacement part for it. I had this fitted and a piston has a slightly different top to it. However this seem to make the battling a little bit worse on my car. So all I can assume is that it is related to the piston. My Indy has no other explanation for this and he knows these cars inside out. I�ve had a bores checked their fine So it is nothing to do with scoring. I�ve had all my cam chain tensioners changed too. And I�m thinking that if it was the I MS that this would�ve failed as I�ve driven it hard more than 4000 miles since I noticed the rattle. So fingers crossed for both of us. Interestingly - my car has also had a gundo hack. Hmmmmm

No, not gotten worse. If I drive off immediately the noise isn�t there. And after 2-3 mins, and when fully warmed up, purrs like a kitten. I haven�t bothered to figure out where the noise comes from since I�ve heard quite a few of these early 996s make this same noise, I figured it�s probably not something critical or unique to my car.

My car has made this noise since September 2016. It is true, if I let the car sit it will make the noise as it warms up, but if I drive off slowly and keep the revs down it is gone by the first stop sign (30 seconds or so). No unusual oil consumption, no soot and nothing in the oil. I have basically stopped worrying about it and have been using it as a countdown to when I can get a fresh engine in her and drive her for 20+ more years. The noise sounds very unique in person and I have only truly heard it come from 99s. It does not sound like everyone else's bore scoring videos (no matter how hard they try to convince you) and this thread shows how crazy m96 owners can be with replies stating your car is toast and to get an engine rebuild stat. I definitely recommend looking into it if your car develops the noise just in case it is something as simple as your exhaust system or even metal fluid lines knocking against the engine bay due to a broken bracket (yes.. I have followed all the threads..). Regardless, I have become numb to this sound that initially resulted in in 7 lbs lost due to stress. Plus, the sound is not really there all summer unless we get a very cool morning. Here is what I have done in an attempt to diagnose and fix the issue: 1. Borescope check through spark plug holes. 2. Second bore scope check through both spark plug holes and bottom of sump (different more experienced tech). Tech mentioned the sump was one of the cleanest he has seen. 3. Muffler replacement. 4. One service to replace the following: clutch, flywheel, IMS, RMS and chain tensioners. All this work and 3 different techs and still no clue what is wrong. Guess I will just continue to daily drive it all spring/summer.. I hope you guys can find a simple solution for your cars!

Twitchett, looks like you have read all the posts and have tried quite a few things. I still have yet to use a stethoscope on the cats or to track down the problem (as Ahsai suggested). I have stopped worrying about it for a few reasons. The oil filter is almost always pristine. The only time it wasn't pristine was after 2 track days, presumably the only track days my car has ever seen in its life. Each track day, the engine was run to redline, full WOT, drive it like I stole it, all day, for a total of ten 30-minute sessions on the track over both days in higher heat as well). The only bits in the filter after those days were posted above (no metal). If it were a bearing on the crank or rods, bore scoring, or an imminent IMS failure, metal would probably show up. If it were chain tensioner pads, I'd suspect I'd see more plastic. My cam deviation numbers according to Durametric were -2/-4 when cold, and -3/-3 (right/left) when warming up and warmed up, respectively, and that's within spec. My car probably uses a quart (Mobil 1 0w-40) every 4-5,000 miles, never any check engine lights, pulls strong, etc. The inside of the engine looks so shiny it's blinding. I'm not saying there couldn't be a big problem lurking, but I could spend a lot of money trying to fix it - as many others have tried, thinking they had stuck lifters, mufflers, cats, chain tensioners, etc. But many performing that work resulted in the same thing you saw: no change! I don't believe that switching oil or adding an oil additive would fix an issue, just mask it. I plan to just keep driving it and not worry. Maybe I feel like my car is closer in spirit to a 996tt than it really is, even though those [Mezger] engines are really completely different and nothing alike. My car just might like to pretend it has the same marbels sound at cold start that those engines often have (and there's nothing wrong with many of those either). I'll probably get a stethiscope one day and try to find at least where the source is coming from.

Yep....my 99 still does this and like others have said, it goes away after a 30 second drive from cold, it is only present during idle after a cold start up. Put the slightest amount of heat into the engine and it goes away. I sleep well at night not troubleshooting it.

Hey guys, I have a 3/99 996 and I have the exact same sound. All good health reports from my mechanic as well, did you ever figure it out?

Nope. I start the car and drive off immediately keeping revs around 2,000 and I don�t have the noise. I probably could have the tensioners replaced, but not convinced it will solve the issue.

My original motor had a bad ims tensioner and would rattle for 3-5 sec at start up. Not sure if this is what u r hearing?

I guess depends on the noise its emitting... Its now been over 15K miles with this noise and I've driven it HARD. No oil consumption, no smoke on startup, scoping through the plug holes everything looks great, 5W-50 Porsche classic oil is being used. There does not seem to be any power loss over this time. In fact, I've performed a lot of service work and cooling system work and it seems to be a little more responsive. I'm talking freer revving and feels like a little more power. May be placebo making me feel good for spending several thousand on maintenance :-)

Quotes source post: 14553865

You can clearly hear yours in the second video for sure! Was it bore scoring? Did you have it repaired?

I have an early build 99 and have a similar sound, but mine is much less pronounced. It always happens at a cold start and goes away almost immediately after driving. Being a newb, I was freaking out but have been told by several people that it is "normal". Very curious to see what the diagnosis is!

Quotes source post: 18321976

I would agree! There are arm chair mechanics that really know nothing and scare folks into thinking they have a major problem. If you listen to any car you can hear "knocking"......its when it's pronounced...is when you have any issue. Drive your car and do your maintenance and enjoy it.

Quotes source post: 18321995

I hear you. I am done worrying about it the car uses 0 oil, the bores are clean, runs amazing and I am now finally getting settled in and used to the car. I think I am finally over the "oh my god what have I done phase" and look forward to long ownership! Thanks!

Mine has never gone away, but I don't let it occur as I put a load on it as soon as I start it. Then after just a block or two it won't make the noise. I believe it could be the onset of bore scoring on my car. I have not scoped the cylinders and don't really care about that. If anything happens to the engine or original IMS bearing, I'll just buy a short block from Porsche and replace it. My car runs awesome as-is.

Same here. I think my car might also have early onset of bore scoring. With 69k miles, though, after I put on 20k miles over the last 5 years, I�m not worried about it getting much worse anytime soon. By this age, the cylinder bores are probably in average condition that�s appropriate for cars like it. If I keep tracking it, I can expect a shorter lifespan. I keep the car in a 55F heated garage, so cold starts aren�t freezing cold, and I change the oil often.

For people experiencing the issue in this thread, try pushing in the clutch to isolate whether its the dual mass flywheel. My flywheel makes this noise at idle.

I tried that, and also tried removing the serpentine belt, but it�s not that.

Man - these threads are always like thriller novels. Start out with simple premise - then go to "DON'T DRIVE THE CAR" - then years later, all good! On my new to me 1999 with 99k. I hear similar knocking (I think similar) after start up. Start up has a different sound. Rate my engine sound? (full inspection schedule in 2 weeks). You Tube You Tube

^^ Yep, that�s the sound! The only thing I haven�t checked is the t he piston and spring from the oil pressure relief valve. I do remember reading about this in many threads over the years. You Tube

My car with 136k has the identical sound at start up. I think more importantly what does it sound like after being driven and brought up to temp (mid needle on the gauge)? Mine quiets down significantly. My mechanic doesn�t suspect scoring and the previous owner had it scoped at 128k with no true signs or scoring (although he did not have this documented). Keep us updated please.

Quotes source post: 18494842

What's nuts is that is the same exact sound FSI's highlights in their video. And their first proof in scoring. So I don't know what to think now. You seem to have survived five years with no issues.

Quotes source post: 18492810

Fwiw, my 9/98 build �99 has always sounded like this. I�ve owned her for 8 years and 40k miles. She now has 102,000 miles. New tensioners and the updated spring didn�t do anything. Mine makes the noise after startup and then never again after the engine goes above ~1800rpm. The sound is most noticeable when standing at the drivers door but hardly discernible at the rear of the car. I scoped the cylinders about 3 years ago and everything looked clean. Oil changes every 6 months (Driven DT40) as well as UOA with every oil change. She doesn�t burn oil and never soots the pipes. I gave up long ago on figuring out what could be causing it.

Mine still does it, but I just drive it as soon as I start it up and the noise goes away as fast as I drive it away. One block under load and it doesn't make the noise.

Mike, did you ever use a stethoscope to listen to the cats??? Also, before throwing the baby out with the bath water , use some Sea-Foam down the intake as directed to clean the carbon from the piston tops..... On the m96 the piston is very very close to the head and it only takes a little carbon build-up on the piston to tap the head ..When the engine is first started the piston can rock a little in the bore until it heats up and gets fatter and doesn't rock as much. The little rocking can cause the piston to tap the head if there is carbon build-up on the top... I have seen quite a few things cause this exact tapping noise, including bore-scoring .PLEASE check all of them first before condemning the engine..( although I do agree that lifters are the last thing to check/possibility ) ..