I have a 1992 Bmw 325is. My rear driver brake caliper is scraping my rotor on the side facing away from the car. I took off my tire and when the car is jacked up, the caliper is not even touching the rotor at all. But as soon as I lower the jack and the car is stable on the ground again, it creaks and screeches and the caliper is once again right against the rotor. HELP!