what is causing a knocking noise near drivers side wheel?

I have a C2, and for a while now there has been a knocking noise by drivers side front wheel? It's most noticeable going over bumps. The drive of car seems quite hard, and recently had passenger side front coil spring replaced aswell as a mounting plate. At the time I asked garage to see if they knew what this. was and was told they couldn't find anything wrong. If they car is stationary and I rock car side to side you can hear it. I'm baffled as to what it can be. Ideas?

Marsh
February 2010