I got the same problem, got brakes aparts, was told that semi metalic brake pads on slotted rotors would be bad, I just put ceramics on it tonite, no change, I think it's the rear brakes, its just fooling me when I drive it and break, strange, that when I use the parking breake the grinding doesn't reproduce but I think the parking break engages differently; what the heck; I had a front wheel bearings repacked last year, I jsut don't see how that could be it, when I have the car up in the air, there doesn't seem to be any significant play