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 4MATIC Worn Sway Bar Link Joints Causing Knocking Over Bumps
Mercedes-Benz C320 4MATIC Problem
Average Mileage: 133,000 mi (122,000 mi - 144,000 mi)
Visitor, 2004 Mercedes-Benz C320 4MATIC, 144,000 mi
Loud knocking noise over driver's side when hitting a bump in the road, knock not present at higher speeds. Replacing the sway bar end links solved the problem, car is whisper quiet now. Price was $486.60 for both sides at an independent shop.
Visitor, 2004 Mercedes-Benz C320 4MATIC, 122,000 mi