Wheel bearings, worn/trashed suspension components, etc will cause knocking.

Before getting carried away, CHECK YOUR LUGNUTS!!!! I had exactly what you describe and it was from a tire shop not torquing down the lug nuts!

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]