Rattling on 1990 300SL
 

My moms car has been making a pretty loud rattling noise. The noise happens after she has driven it for a little while and the car is sitting still at idle in Drive. When the car is in park it does not rattle. Our mechanic said it needed new motor mounts and I thought he was right but he changed them and the noise hasn't really gone away. I haven't tried to track the noise down myself yet but I was wondering if anyone has had this type of problem. The car is a 1990 300 SL. thanks

Hi,
See my recent posts. I had a similar problem. I found two sources of noise. First a rattling noise from a loose timing chain due to a jammed chain tensioner. Secondly from a vibrating Fan Belt Tensioner Damper. It is on the right side of engine close to the belt and behind the water pump pully. With engine running and somebody's help keeping it in R, carefully and firmly press on the top of the damper and see if the noise goes away. Thanks to the Forum fans who helped me finding the cause.

Could be an exhaust heat shield got a little bent and is rattling against the exhaust system.
Gilly

Follow up
 

For your information, I changed the "fan belt tensioner damper" today. The noise is defenitely gone.

Sean