Engine tapping under acceleration?

Hi all, New to me 2004 c4s cab with 23,000 miles (now 25,800 as my daily driver) recently started making a tapping noise on acceleration that I hear best between 2,000 and 3,000 RPM. It's not present at idle or cold start. Even not under load I hear the noise between 2K and 3K on the tach. No noticeable issue with acceleration. Car just goes zoom. Car has had no major repairs. Original IMS bearing which I plan to have retrofitted with the LN kit soon. Oil has been changed when I bought it and then again after 1,000 miles just to get a look at the filter (curiosity more than anything else). Just a tiny flake or two of non ferrous stuff. Magnetic drain plug is clean. Flushed the coolant. Flushed the trannsmission and front diff. Searching found no answer to this on RL. Doesn't sound like the typical "piston slap," since I don't hear mine at idle. Thanks in advance.

There was a question over on the 986 Forum regarding tapping (rattle) @ between 2800 - 3200 rpm and Jake Raby suggested it could be cam chain(s) stretched, but a chain would have to be pretty loose to actually hear it.... 986 Forum - for Porsche Boxster Owners and Others > Porsche Boxsters Chain rattle at 3K - Do they all do it? If it is "piston slap" a borascope will be able to confirm it - what's your oil consumption like?

Oil consumption is not much at all. The level has remained fairly consistent and I have yet to add oil between oil changes. I read that thread over on 986forum.com. Thank you for pointing me in that direction, but it seems that the stretched cam chain would also be accompanied by a rattle/tap at start up. This doesn't occur. The rattle is only present when the engine is at operating temperature and only between 2,000 and 3,000 RPMs. It may be present above 3,000, but I suppose things get s bit loud and obscures the noise. I will keep this in mind when I have my IMS bearing retrofitted in a few weeks and discuss with the shop. At the risk of sparking an oil debate, I use Mobil 1 0-40. Any other ideas?

I've heard ideas about exhaust manifold leaks at certain temperatures that can make a tapping noise, never heard one though... and also maybe want to look into your cats. Sometimes a chunk is dislodged but still in place and will only make noise at a certain temp. Bring the car up to temp and tap your cats with a rubber mallet. I'd say start with the easy stuff and work your way up to the more intrusive... Also a good idea to have someone else rev the engine up and try to pinpoint the noise from the outside of the car.

I'm in agreement with pordlanzer. Doesn't read like an internal engine noise problem. Reads more like an exhaust or heat shield problem. My best advice is to have the car listened to by an experienced tech. In the outside chance this is a prelude to something more serious I'd avoid driving the car any until after the tech has given a listen and you know what's going on and it has been addressed.

Thanks all for your help. Will take it in and have the tech look at it when the IMS is done. Unfortunately they're booked solid until March. Will also post back when it is all done and hopefully will have an answer. For what it's worth I did get under the car and listened around (no stethoscope) while the wife pressed on the accelerator. I heard no noises. Looked around the exhaust system, at the headers, various flanges, cats, mufflers, and saw no obvious extra soot (or any soot for that matter), felt no puffs, nor heard any leaks... But who am I? I just do simple routine maintenance items and my day job is nowhere near as complicated. I will of course defer to the more experienced here and at the shop!

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Just to be clear, I'd advise you to have this looked into ASAP. I would not wait until you take the car in to have the IMSB upgrade done. From what I read the shop is booked up until March. That's 3 months away. And 3 months is too long to continue to use the car with what may be an internal engine noise. If it is an internal engine noise -- my layman's opinion it is not notwithstanding -- no internal engine noise ever got better with more engine usage.

Sometimes it is as simple as a loose spark plug. Check the plugs and make sure they are all snugged up.

Could also be something in the drivetrain - a wheel bearing or half-shaft, maybe? - that only acts up during acceleration...

Took it to my Indy and asked him to look into it. He drove it around and said he does hear it, but unsure what it is. He offered that it could be the oil I'm using, saying that 0-40 is sometimes accompanied by noises and recommended that I switch to 5-40 at the next oil change. Come to think of it I hadn't noticed it when I first brought the car home, and I guess I'm sort of convincing myself that I only heard it after I changed the oil to 0-40. Perhaps I'll change it now and see if that makes it go away, but I'm thinking the dealer is the next stop.

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Neither of my engines knock or tick when running 0w-40 oil. However, I change the oil at 5K miles. Now both engines get quieter overall after changing the oil. Even thought the oil has just 5K miles it does get a bit diluted with combustion byproducts and I notice the difference when changing the oil. I have to point out the noise is only present once the engine is warmed up, so switching from 0w-40 to 5w-40 still have the engine filled with "40" oil. I suspect if oil is indeed the cause of the noise that just replacing the "old" 0w-40 oil with fresh 0w-40 oil will have the engine quiet (or quieter) once again. If you believe 0w-40 or really "40" oil is too "thin" then maybe you need to consider running 5w-50 (not a typo for 15w-50!) oil. I use this in both of my cars now. However, I have to point out I live in a warmer region of the country where even in winter it seldom gets below freezing so 5w-50 year 'round is ok. Up in PA where you live if you drive your car year 'round 0w-40 might be quite appropriate given the ambient temperature there during the winter months.

I've only had the car for a little over 2,000 miles. I had changed the oil once to 0-40 when i bought it and then changed it once more about 1,000 miles after that. I was curious to see what I would find in the filter. My routine has always been to change my oil every 5,000 miles, no matter what any oil analysis says. Neither the filter that came with the car nor the one I changed at 1,000 miles with fresh 0-40 showed anything too surprising. Maybe a small fleck or two, non ferrous. No plastic bits. So I was fairly happy with what I saw. I chose 0-40 with some trepidation as my previous e60 BMW was always 5-40 and was fine even here in PA. Heck my old e46 m3 used to be okay with 10-60 too, but all the internet chatter seemed to be strongly in favor of 0-40 for the northern tundra climate. Thank you all very much for your help and advice. I will try out the 5-40 and see if that helps with quieting things down. On my way to the shop today it did sound quieter, but I hadn't changed anything so I'm sure it was all in my head. These 996 cars are awesome (way better than any BMW I've ever owned) but they definitely have their quirks.

I don't find my 996 way better than a BMW M. Maybe as a pure sports car. But honestly if j had to pick just one car I would keep my E39 M5 and let the 911 go in a heartbeat. As much as I do enjoy the 996 - it really is a fantastic car. But the M5 is my favorite car of the 40ish I've owned.

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The e39 m5 is a great car. I would love to own one at some point in life, but now is not the right time for me. Don't get me wrong, the e46 m3 was also a great car (I had it for 10 years and drove the snuff out of it on the weekends), but my 996 just edges it out all around. It's a matter of opinion frankly. If it wasn't for the wife, that m3 would still be in the garage......... Next to my 996... And maybe an e39 m5 or a... 964 or 993? Life is too short.

Just wanted to update you guys... Had the IMS bearing upgraded to the LN single row pro, RMS, clutch, and AOS replaced over the weekend. The OE bearing was completely intact and the flange cover was dry. The RMS was a little wet, but intact when they took it out. Filter cartridge was clean. The AOS was fine but I decided to have it replaced since they were there anyway (same rationale for the clutch). As part of the service the oil was changed to a blend of 15-50 and 0-40 and the noise I was hearing between 2,000 and 3,000 RPM has definitely quieted down. Frankly it was difficult for me to hear at all if I wasn't trying so hard. I suppose having gone through all this, it would be silly to think the car has a new lease on life, but it does go a long way in calming some the 996-associated neuroses I've developed in reading RL threads. Let the other 25 modes of failure commence!

CV, I see a Mechanics Stethoscope in your future? You can get an old fashioned one for less than $10 . It requires some skill/experience to use it without blowing an ear drum. Hint -don't bang the tip on anything ! If you can give us the location of the noise ,it would narrow down our speculation.Your 'mechanic' did not try this??? http://www.walmart.com/ip/PROTO-JFP5...scope/40833243 http://www.walmart.com/ip/PROTO-JFP5...scope/40833243

I found turning up the radio solves most of the noises I hear from time to time.

From reading your posts you think its an engine noise not a drive train noise, right? In other words, you can hear the noise while in neutral, revving fully warmed engine to 2500-3500 rpm? Does it sound like a valve train noise? Seems like a very low mileage engine to have chain slap from worn guides but maybe it has some gummed up lifters from sever lack of use? Is there an immediate noise on start or at idle? Taking the belt off and running might help isolate the noise. A video would be helpful.

I think I figured out what it was...

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Definitely engine and at first thought it was valve train, but no sound on start up or cold. Just warm and between 2,000 and 3,000 RPM with or without load (hear it in neutral). Sound can also only be heard inside cabin. Can't hear it outside unless, perhaps, I use a car stethoscope. It's become considerably quieter since switching to the somewhat thicker oil (the 15w-50 blend with 0w-40). In fact I struggle a bit to hear it but still can hear it a bit. I had previously used 0w-40 alone. At this point, several techs (in 3 states -- seriously!) have looked, listened, driven, but that's about it and no one seems terribly interested in carrying out further investigations. They all hear it and have no idea what it is. The suggestion of using a bore scope to look for signs of piston slap was met with an OMG-type response.

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I agree. I'm pretty sure it's probably just hamster that got sucked into the intake manifold and it's just knocking at it trying to get out. Haha.

If you want a permanent solution for a quite engine, try Jakes JGDT40 / Driven oil for the M96. You will notice an immediate improvement. Seriously. Ask anyone that's switched to it from the Mobile 1 garbage oil.

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Kind of funny but the Dodge Challenger Scat Pack and Hellcat owners are being advised both by their dealers and factory rep in one case and other owners to use Mobil 1 0w-40 to cure the "Hemi" tick.