R129 strange transmission noise
 

I noticed a strange noise from the transmission today. It is very difficult to descrive but I will give it a go.

The noise occurs when pulling away from a stop. It occurs at approximately 10mph. It is like a graunching, grinding, rumble of a noise. It lasts about one second. I'm sure I can also feel it. It seems to come from the left hand rear side of the car (left hand when sitting in it).

What could it be? Differential? Transmission? The car has 70k miles on it. The transmission fluid was changed about 1 month ago. Makes no difference whether the car is cold or hot.

Please help!

Further observations:

The noise happens at about 2,000rpm. It can be felt through the floor in the front of the left hand side footwell, near the transmission tunnel. I think this must be transmission related, although I note the exhaust runs very close to this location. The exhaust is not blowing.

There are sheetmetal shields above and around the exhaust system, attached to the underbody. These are occasionally found bent and touching or within about 1mm of touching the exhaust systems and under certain conditions will contact and vibrate against the exhaust and make weird noises like this.

Gilly

Gilly, thanks. Now you've said it, I'm pretty sure that's what it is. I hadn't thought of the heat shield, but the noise is exactly the same as a noise my dad's Audi made with a loose shield years ago. It's going in on Wednesday.

JJ
Anyway you can just look under there yourself and look? Maybe your dealer won't charge you for bending a shield back, maybe they will. They'll do the same thing you could do yourself, just bend it back where it was by hand.......

Gilly

I'll do that Gilly. The car is going in anyway for a load of other trivial stuff: evap temp sensor, outside temp sensor, wing mirror glass, a dashboard bulb and some other adjustments.

Hopefully that's what it is JJ. That shield can get damaged easily.

I ripped mine in half (almost completely) when I hit a deep puddle during a monsoon.