Affecting: Pretty much every Citroen Peugeot Renault Fiat & Alfa
The antiroll bar link (rod) ball joints have probably become worn. Like any worn ball joint, the ball will rattle around inside it's cup when agitated. There is no cure other than to replace the rod. The vehicle will have an Anti roll bar running laterally across the suspension from one side to the other. The rod links the bar to the lower suspension arm or track control arm. Most versions will be a metal (plastic on some ZX/306's) rod with a ball joint at each end. Early ZX's have a small unit shaped like a figure '8', whereas the 407 and C5 have sort of lever arm arrangement. Some Fiats, Alfas and most Renaults have a pin & bushes arrangement. But, they all wear out just the same.