Left rear caliper makes loud noise when backing up...

[c-rad]

Whenever I back up, the back rear caliper makes a loud vibrating sound. But...if I touch the brakes or pull the ebrake 1/2 way up, the sound goes away. WTF could be making this happen?

[Meantime]

I had the same problem. From the marks on the rotor it looked like the pad was getting "caught" when the car was going in reverse. If I press hard on the brakes before going in reverse, it stops the vibrating from happening - I guess it resets the pad in the caliper and stops it from scraping against the rotor.