The sway bar end link joints may wear and cause a knocking noise over bumps. Loose or warn links should be replaced to correct this type of noise.Google+
Car Problem Reports
Mercedes-Benz C320 Worn Sway Bar Link Joints Causing Knocking Over Bumps
Mercedes-Benz C320 Problem
Average Mileage: 121,333 mi (74,000 mi - 200,000 mi)
Visitor, 2001 Mercedes-Benz C320, 200,000 mi
Sure enough after looking at all the lower front suspension, the sway-bar link joint was loose in its fitting. The rubber boot was in perfect condition so from an outward glance you would not have known there was any problem. I replaced both sides to ensure that noise would not come a calling anytime soon. Was an easy job to do myself. After I completed that task I removed each sway-bar shell, that attaches the sway-bar to the chassis by some torx bolts, and applied silicon lube within the rubber bush. This fixed the squeaking noise that emanated from small movements of the car over lightly undulating surfaces.
Was a great relief to drive the car around without all the knocking and squeaking :)