How to fix a rear suspension knock on 2008 C5 VTR?

My C5 2008 2.0ltr deisel is a lovely car. The best Citroen I have owned and I have had Citroens since 1982. Its powerful, comfortable, economical and quiet. Unfortunately it has develped an annoying knock or rattle from the off side rear suspension when running over uneven road surfaces or shallow potholes or dropped grids. It occurs after encountering one of these obstacles at slow speed and the familiar thump of the suspension is followed by knock or rattle. When on motorways and fast roads the fault is not noticable at all nor when the car is rocked up and down whilst stationary. Someone said it could be the suspension link arm bushes, but having looked at the rear suspension (steel sprung not pneumatic) there are lots of link rods and what could be ball joints. I am reluctant to take it in until I know a bit more about the fault. Any advice would be welcome as would possible sources of literature or diagarms about the C5 suspension etc.