I have a 2007 Mazda 6. I am getting a metal on metal noise coming from the brake pad area, I think, whenever I back out of my drive way and pull forward. As soon as I apply the brakes for the first time at a stop sign I can hear a metal on metal noise coming from the dirver and passenger side brake disc area. It only happens if I go in reverse, drive forward, and apply the brakes. I've taken it to two different repair places and the can't seem to find a problem. Any ideas?