Interior noise

I'm not sure if I'm getting old, or what, but my 996 seems incredibly loud. With windows up, at 70 mph, I'm seeing 84 decibels on the "Sound Meter" Droid app. I realize that it's not the most accurate meter, but I'm seeing 74 decibels in my fiancee's e39 M5 at similar speeds. This isn't normal, is it? It's a 2003 C2 Coupe 6 speed. Engine seems to run fine, good oil pressure, pulls hard, last two oil changes showed filters that were clear of debris.

Something tells me your 996 days are over...

I never measured the interior noise in my 996 C4S with a sound meter, but it was loud enough at highway speed that I couldn't have a hands-free telephone conversation. The combination of engine noise, road noise and wind noise is pretty loud...

Can you tell what is producing the most noise? Engine, trans, tires, or wind? The loudest sound from the engine should be the exhaust, or possibly the mechanical valvetrain noise. Manual trans can have failing bearings that "whine" and cause substantial noise. Tires are the most common culprit for noise at speed. Worn tires are particularly bad for noise, and all brands are different in the amount of tire noise they produce. Excessive wind noise can be caused by rubber seals that are in poor condition, are missing, or are mis-aligned. Do your windows seal tightly? Do you know anyone else with a similar car who could ride along and compare noise levels? I find my '01 C4 cab to be more quiet than my '06 Cayman. The main difference being that the Cayman has considerable mechanical noise and obviously less sound deadening for "road noise" (tires, wind, etc).

Got to agree with Spokyman. Maybe it is something in particular that is making a lot of noise...I'm thinking tires. Recently did a run on the interstate running northwards of 70 and I could have a pleasant conversation with my wife. It really is quite comfortable at speed, but then again I love the sound of that flat six purring away behind me.

My 04 targa is very noisy as well, especially on grooved concrete freeways. On asphalt, its much quieter. I am fairly certain it is the tires. The PO put on Michelin Sport AS3 in 19". In reading reviews, people complained about tire noise. One of these days i will put the rear 18's from my Boxster on it and see if the noise drops

My 2002 Targa is extremely loud at freeway speeds. It's the Sumitumo HTR ZIII tires.

My car had excessive road noise when I bought it. It was a bad front wheel bearing...not the tires.

A difference of 10db between two cars is a LARGE delta, though, so I'd wonder if something is up: * Alignment/balance * A gappy window or door seal * Wheel bearing Without hearing what kind of noise you're hearing, it's almost impossible to guess. My 996 is certainly louder than our Murano, but I don't think it's any louder than my Corvette. At speeds above 85, it starts to get really loud, but at 70mph, 84db seems HIGH. For comparison, sounds in the 80db range: Garbage disposal, dishwasher, average factory, freight train (at 15 meters). Car wash at 20 ft (89 dB); propeller plane flyover at 1000 ft (88 dB); diesel truck 40 mph at 50 ft (84 dB); diesel train at 45 mph at 100 ft (83 dB). Food blender (88 dB); milling machine (85 dB); garbage disposal (80 dB).

Quotes source post: 11810829

Yeah, I didn't think I'd gotten that old. Noise is directly related to the engine, rpm's go up, noise goes up. I'm having it checked out at R&D auto, tomorrow. It's definitely more on the bass side.

I'm going to test my car this weekend as I am curious.

Meanwhile, I wish I could further amplify my FisterD's

Quotes source post: 11811764

Cut a hole in the rear firewall. if you mean amplify it to others outside, get cat-bypass pipes.

My passenger side window sometimes doesn't drop down the 1/2" or so as the door is closing to allow the window to rise back up into the weatherstripping. So, it hangs up on the outside of the weatherstripping and has a small gap at the top of the window. It gets extremely loud at speed. Easy fix - after the door is closed, roll the window down about 2 inches and then back up.

I have notice this as well in my 99 C2. I am blaming the tires as they are old (not worn) and the compound is not as soft as a nice pair of new tires. I have Bridgestone Potenza S-02's on the back and Dunlop Direzza DZ101's on the front. I now have a set of Sumitomo HTR Z III in my shopping cart with Tire Rack.com. Scored exceptionally high in the track tests with a cost of $514 for the set.

Sorry for not providing all the info. My noise is definitely related to the engine. I can get the meter up to 80+ decibels with the car standing still. Just rev the engine to 3k rpm. No difference with the clutch in or out. I've pulled the back bumpers in an attempt to diagnose it, and can't pinpoint the source. The engine sounds fine from outside the car, but there's a knock that's transmitted to the interior of the car. I've put my hand on the heads and the block, and I don't feel any significant vibrations that correspond to the knock. I do feel it in the exhaust, but it doesn't feel strong enough for what gets transmitted into the interior. No signs of an exhaust leak, no signs of misfire, or loose spark plugs. It's been impossible to isolate, so far.

Is your engine mounts original?

No, I recently replaced them with the Function First units. Trans mount was tired, and I added the FF reinforcements, which seemed to help at first. The trans mount didn't show any signs of being torn through, and I'm not feeling vibration when I put my hand on the tunnel by the rear seats. Noise seems to be coming from the right rear corner, but I haven't jumped in back to really chase it down. With luck, the shop will find it. When they do, I'll definitely report back.

If you have both the FF engine mounts AND the FF harder tranny inserts, that could be the source of your NVH. Was the noise level the same before you put these on?

Quotes source post: 11812690

It may have gotten slightly worse, but definitely not a significant difference. It was still abnormally loud with the factory mounts. I'm totally good with it being louder than the M5, but as mentioned above, 10 db is pretty ridiculous.

Looks like I'm getting the IMS bearing replaced.

Wow, are you saying that your noise is the IMSB? How long has it been making noise? I thought that when these bearings go, you have minutes, maybe just seconds to shut it down before it flies apart.

That's what the shop is saying, but I'm having a really hard time believing it, at this point. Car has been making the noise for a few thousand miles. I've changed the oil, twice and found nothing in the filter. The shop said that they're seeing some decent variation in the cam timing, which is causing them to suspect the bearing. They said they'll let me look at it, when they open it up, and I expect to see another perfect IMS bearing. I'll report back.

Hmm, Could be the IMSB. Might also be a chain tensioner problem??

since the cost to drop and reinstall the tranny is a big part of the cost to replace the IMSB and in order to inspect it you have to drop the tranny, it would be prudent to replace the IMSB even if it looks good today Might as well replace the clutch for the same reason

New clutch, flywheel, AOS, and an LN Engineering IMSB are going in the car, today. The shop pointed out that the dual mass flywheel was out of spec - 16mm of play vs. the allowed limit of 10 mm. Haven't seen the IMS, yet, but I still suspect it's going to be fine. They said that cam timing was out 5 degrees, which has me wondering if there might be an issue with the cam tensioners. Still hoping to get to the bottom of this.

So now the latest is noise automatically = bad IMS? LOL, wonder where people come up with this stuff. What happens after they replace all that and if the noise is still there? Do you get your money back? I'm just waiting for a post on "I took off my front bumper but now there's some strange noises in the back and I suspect it's the IMS..." Keep us updated and aks the shop to see the cam deviations when hooked up to YOUR car via pst2, piwis, durametric... BTW, how many miles on it?

70k miles. Yeah, agreed on the IMS paranoia. If I weren't under the gun, and driving the car to Texas on Wednesday, I would have waited, and just done the work, myself. I hate having to let someone else work on it, but didn't feel comfortable driving ~2k miles with it that way. What's really sad is I'm blowing my coilover budget on this.

Hmm - well, I just got a '99 C2 coupe, so haven't had it long for comparison. But I also have a E39 M5. And I can tell you the M5 is significantly quieter inside. 10db worth at highway speeds? Hard to say, but has to be at least 6... (musician and engineer so I have some concept of dbs)

I can't find it, now, but I read a road test that had the 996 GT3 at 76 or 78 db at 70 mph. The noise I'm hearing is definitely not normal, and I'm hoping that it's the flywheel. Shop called and "the bearing had some play, and they suspect the flywheel was the issue" which for me translates to "the bearing was fine, we just wanted to sooth the pain of paying for a part that really didn't need replacement." I don't regret putting the LN unit in there, but the amount of hype surrounding these is ludicrous. At least I can bump the price by $2k, if I ever go to sell, now.

Could it be a loose cat?

Quotes source post: 11820674

It's a possibility, but I couldn't feel vibration in the cat, when I had the rear bumpers off. It was present, even when I took the mufflers off, so not there, either. If the flywheel doesn't fix it, I'm starting to run out of possibilities.

Just take off the 4 wheels and put a new car on them

Quotes source post: 11820661

fasle! It will not increase resale value much if any. But it may help you sell it to a small percentage of gearheads looking for one with this specific maint item addressed. Guys like me. I just bought one with this already done. And I did not pay more for it that examples without - in fact, I paid less for this one compared to other cars I was looking at.

Quotes source post: 11820761

I am partial to the 5 spokes . . .

Make sure if you get the LN to get the paperwork and the door sticker put on and verify that your mechanic did at least some sort of prequalification in writing so when it comes time to sell, you'll have an easier time. Nowadays, it's not just enough to have the IXX retrofit done but to know that it was done to a healthy motor with no prior debris in the oil.

I finally got around to running the noise level app in my 996 - cruising (maintaining speed) @ 79MPH in 4th gear, I was seeing average readings of 61-63db, with peaks of 67 over bumps and stuff. Conditions were not appropriate for pushing the speed higher. Above 90, my car gets MUCH louder due to wind noise - but at a tame freeway speed, I'm definitely not seeing the same sound levels you are. I also have very short tires, a loudish exhaust, and WEVO semi-solid motor mounts, so I would expect my car to be a bit noisier than a stock 996 coupe.

I downloaded a db app and it has a feature to calibrate my Samsung 4S. I drove my Yukon and dialed it in to 72 db (which equates to -6 db). I then ran the 996 in both directions on the highway at 80 mph. It read 76 db. This seems about right right to me. I have seen Porsche 911 tests run about ~76 db. Dan 2003 996

Thanks for the reference points, guys. Schnell, I'm thinking your readings are extremely low, based on what I've read. Dan, Your numbers sound a lot more reasonable to me. IMS, and the other changes did not show an appreciable reduction in noise. Looks like I'll be troubleshooting this one, further, on my own. I want my 6 db back!

So the shop replaced the IMS and flywheel and you're still at square one? Has the car ever been in an accident? Are all weather stripping and trim intact? Did you check the integrity of all rubber plugs in the rear firewall?

Quotes source post: 11832299

The carfax had an incident reported in which the car ended up in a ditch. I've been all over the undercarriage, and the only sign of damage was the right side underbody brace had a very slight crush mark in it. I replaced the brace as a precaution with no joy. Weather stripping and trim are in tact. I'll check on the plugs in the rear firewall. Any chance you have a diagram that would show their locations?

If the car is crabbing, even slightly, due to the mishap involving a ditch, that can produce a crap-ton of road noise.

Quotes source post: 11832642

No crabbing, tracks straight. Plus, the noise can be recreated with the car standing still. Definitely not an alignment or tire noise issue. Body plugs seem like a likely candidate, but I have no idea why someone would pull them. It honestly seems like someone pulled the insulation out of the car, which makes no sense whatsoever. I've checked to see that the rear pad is in the back of the car, and the next step, I think is to just start pulling out more of the interior in the back, to see if something stands out.

Body plugs are at each upper end of the engine bay closest to where the rear seats would be on the other side. Mainly rubber plugs that feed wiring from cabin to engine bay but sometimes they can pop or become loose. Or if PO installed anything that required taking these pieces off, it could've never been put back 100%. Even the slightest cracks can introduce a good amount of noise into the cabin.

Quotes source post: 11832792

If this was my issue, all along, I might just burn a $100 bill in memory of the rest of the money I burned.