My Mercedes-Benz C-Class has developed a front end 'knock' from the passenger side when driving over irregularities in the road, such as potholes, at low speeds. In the past eight months the car has had the drop-links replaced (both) and lower control arms replaced (both).

The MoT two months ago failed to pick anything up and it passed. However, the knock has got noticeably worse in recent weeks. Any ideas what could be causing it?