when i back up and hit the brakes the front left wheel makes a pop then a crack sound, then after going forwardand hitting the brakes for the first time it pops with out the crack sound. there after it wont do it. i've look many times at the brakes, unit bearing, steering, ect. nothing looks to be the matter. i only noticed one thing after putting new rotors on that the holes in the rotor for the wheel studs are bigger then the studs. that is the only thing i can think of that make some kind of sound. but not two sounds, and why not both sides? both sides have kind of same rotors.