it'll probably be the actual hub face itself
new ones cured the problem on the estate bt they were around the £100 each side plus bearings etc

remove the discs and clean the face where it mounts up properly with a wire grinder so that you can see the casting marks in it
it might be worth even knocking the studs out and making sure it's all smoth before getting new studs put back in again (at around 32 per stud it's cheaper than new hubs)