I am going through the same issue with my '07 GT... Inner rear tires worn down to the steel. Had less than 30k miles on it. The middle and outside as well as the front tires could've probably gone to 40k. The tires hadn't been rotated as often as they should have but this still seems like some sort of rear suspension issue. The rear tires seemed to be angled in at the top too much - riding much harder on the inner wall than on the outer. Again, less than 30k miles on it... I'm very frustrated as to what could have worn this badly already. I got new tires and an alignment. The angle in the rear wheels is still there