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

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W126 1983 300SD 286,000 miles and ticking
Baby blue exterior Grey MB tex
Recent work:
Replaced air cleaner mounting brackets and heat shields
Replaced alternator, fan and power steering belts
Replaced positive battery terminal
Replaced negative battery terminal and cord
New Duralast Battery

My car needs work.