I've got a 1993 306 XTDT. I think it's suffering from the classic shot rear subframe mounts. It is up in the air with wheels off and if I kick the hub assembly down sharply there is a knocking noise. When underneath I can't make out if the flex in the mount is normal when hub is kicked or if the knock is coming from there. It certainly isn't obviously buggered. Any tips to avoid a pointless renewal?