Citroen C5 front suspension clunking/rattling

A quite loud rattle/clunk on passenger side when on rough roads. Local garage can't find the problem - wait for it to get worse. It already sounds as if something could drop off. Sound is heavier than tinny - I wondered if the brake pads were loose - maybe spring not fitted, but htey say pads are fine, front and back. Difficult to isolate as sound appears to come from underneath the car - they checked for loose heat guards .