I get squeaks and creaks from all four corners of my 91 300SE (W126). The front right was the worst particularly when a wheel was out of balance. I tightened the nuts that hold the dash to the chassis (which were pretty tight to begin with) and that cleared 80-90% of the noise. It might have been the nuts or the trim that had to come off to get to the nuts. Whatever it was, it was worth half an hour.

The next step is to drive without the pilar trim. If it's quiet without the trim, then I'll load up on felt tape.

Oh, make sure you don't have coins or anything that might be rattling in the glove box.

I sure hope I don't have welds failing in all four corners.

Sixto
91 300SE