I have a 1990 Audi 100 and have a problem with noise intrusion into the cabin.
It is an irritating drone which does not change with speed and is ever-present when moving and occurs at all times, both driving straight ahead and going round bends.
The exhaust is not leaking, both front bearings have been replaced without improvement to the sound and three garages have been unable to find anything which might be causing the noise.
It sounds as though noise from the engine or transmission is not being isolated from the bodywork effectively, so transmitting into the cabin. The rear bearings are also fine and engine and transmission mounts appear ok.Tyres have been changed without improvement.

Sorry for the long post, but does anyone have any ideas what this could be as it's spoiling my fun !

Does the exhaust system touch the body anywhere? Are rubber mountings used for the exhaust system? Do you have both of the mufflers in place?

My car: 1988 5000CSTQ (5 speed manual transmission)

I found that a surprising amount of gear whine was entering the cabin via the shift boot. I reduced it by inserting carefully cut pieces of closed cell neoprene foam sheet about 3/8" thick beneath the shift boot and around the shift lever.

I also deadened and sound treated many sheet metal panels, so the car cabin is now nice and quiet.


Read "http://sounddeadenershowdown.com" and have a read and maybe ask your question on one of these forums:<ul><li><a href="http://www.secondskinaudio.com/forums/">http://www.secondskinaudio.com/forums/</a</li></ul>

Thanks for your replies so far.

The car is automatic transmission. The exhaust has been checked out; all mufflers are in place,the exhaust does not touch the body and all rubber mounts are in place.

I've just been out in the car again and the noise is definitely from the engine compartment area and sounds like a rubber bush has failed somewhere, leading to transmission noise coming into the cabin...trouble is, no garage can find anything wrong.

Keep the thoughts coming as I'm willing to try anything.

Thanks,

Don.

the noise is only when moving, not when stopped? in all gears including reverse and low gears?
I dont have a ton of experience with automatics.. but if above is also the case then Id suggest checking either:

A. any bearings between the transmission and the torque converter, or the converter itself

or

B. my other thought is, if its even when parked, maybe even something like the fuel distributer [i cant remember offhand if yours has that?] has excessive vibration or its mounting has worn out.
Or something else associated with the fuel delivery system, since that doesnt change with engine rpm or drivetrain speed.

thats all I can think of at the moment

Thanks for your reply.

Yes, this occurs only when moving, and in any gear, but the sound only becomes noticeable at speeds above 25 mph.
Sound is just the same when I slip the autobox into neutral.

The car has got through seven wheelbearings in three years {!!!}, two each for both rear wheels and 2 for the n/s/f and 1 for the o/s/f. Three garages have told me the bearings are fine but I'm beginning to wonder whether the bearing can appear ok when up on a ramp, but not ok when the weight of the car is on it ?

If that is the case the car will sadly have to go.... I can't afford to replace bearings every 5,000 miles.

Don

All mounts checked and in order. Any more ideas anyone, please ?

I have finally found a mechanic who has diagnosed the problem.
Even though there is no play when rocking the road wheel, this noise is down to a bad bearing.
The mechanic jacked the front of the car up on one side and with the engine running the drone could be heard from the wheel which was rotating in the air. Press the brake and the noise stopped too.
New bearing due to be fitted this Friday...hope it lasts longer than the 14 months the bad one lasted, and that was allegedly a genuine Audi part.