I had the same problem the car seemed to feel unstable going in to corners and seemed to pull to one side a lot I changed most of my front suspension and couldn't find the problem then I thought it was the rear beam checked all of that and it was fine. I had nothing else to change so was getting pretty fed up. But then I decided to replace my rear discs and then suddenly my car came back to life and now feels better than ever so I'm confident your problem is the rear bearing I bought mtec discs in black with new bearings for about £160 and fitted them myself in two hours