Road & Engine Noise Intrusion: w126

[kennysin]

I have recently noticed increasing external noise levels, which seems to be mainly emanating from the bulkhead, especially the central air-con vents. Closing the central vent seems to reduce the noise level.

I am considering stripping the dashboard to investigate and possible add some damping sheets or insulation. I am hoping that it is a problem with the ducting, and not corrosion. There is no water leak to suggest that though.

Any suggestions as to the cause? The noise level was especially apparent after I sat in a w124 which was very quiet in comparison.

[Hocky]

Was the noise apparent before or you just noticed it because you found the W124 a lot quieter inside? It doesn't seem to make sense that noise should suddenly appear unless something between the engine bay and the cabin has fallen off. I have driven a late W124 which was 1994 I think and it was very quiet. It was a E200. I drive a W202 now also 1994 and it is not very quiet inside! I can hear the engine which is not a quiet one though the 1998 version "purrs". I can also hear the acceleration and the muffler roar as we accelerate. The muffler is not quiet too even though only the Cat is aftermarket. I can also hear the tyre roar on the rougher road surfaces. A Lexus would be a lot quieter.

[kennysin]

Thanks for the comments.

I had recently changed my tyres from 205 to 225 on the same rims. Despite the broader profile, tyre roar was decent but bump suppression less. However, I noticed wheel bearing wear and changed all 4 bearings which eliminated the noise.

Now that the background noise from the wheel bearing and tyres were gone, I noticed increased external noise especially from the dashboard vent. It seems to particularly carry high frequency sound i.e. exhaust high pitch rasp and wind turbulence. The funny thing was that by closing the central air-vent, the sound was considerable muffled.

The w124 I drove was a 1992 260E in stock soundproofing. I agree that I may have noticed the difference only after driving it. It is not excessively loud, but again I wonder if it is worth the effort of dismantling the dash.

[Hocky]

From your description it would seem that something has fallen off inside the dash to allow the noise into the cabin which was not there before. Do you have some kind of filter in there in your model? Could this be in the chain of airflow from the engine bay/aircon location into the dash and out of the airvent? If so could this have dropped? Can't think of anything else. Anyone out there who is an expert on this? Sorry I'm only intruding. Mind you if the dealer or indie is going to remove your dash to find out the culprit, be ready to be hit with a big bill. There are many screws and nuts and wires to remove and very time consuming. Double this time as they have to reverse the process to get it back in place. May not be worth the cost and you can best try to ignore it. I reckon my car needs kgs of more sound insulation, but the engine is noisy and you can't silence it. It wasn't designed to be a "quiet" engine. A rubber timing belt would have helped like in the BMW 3 series, but they don't last very long. The cars from Asia all seem to be quieter and have rubber belts which last longer than BMW's. Previously I had lots of tyre noise problems and changed from Goodyears to Bridgestones and solved the noise and vibration problems.