i am having this problem just now the back of the car is all over the road and here in the uk we have SMALL roads haha
i have all brandnew tyres on the car rears are 235/40/17 i now its not the rubber that isnt doing the job .
so i jack the car up and find its the REAR SUBFRAME BUSH that is warn both sides one is worse than the other .
its going to be a full rear end dismantel to change the bushes
i will be doing this in a few weeks and not looking forward to it one bit
here is a photo of the bush and the bush removal tool