I'd check over your rubber bushings, possibly a tie rod or the like. Also if your bushings look alright, consider the ball joints (I had a 190E with a weird sound, slight metal scraping when I hit a bump or dip, I changed the tierods and other parts, but it turned out to be the ball joint). Keep in mind if your driver's side suspension parts look like they are worn and need replacing, the pass. side is not far away and you might want to get both done at one shot.

__________________
1981 300SD (282K) "Blackie" - Gone
1990 190E 2.6 (158K) "Bluey" - Gone
1994 E320 (125K) "Smokey" - Gone
1999 Porsche Boxster (75K)