Intermittent problem when backing down my driveway. While slowly driving down driveway I hear sudden loud noises which sound like something is grabbing the rear brake(s) and may cause serious damage. It corrects itself if I continue moving while in reverse. Emergency brake was released before backing up. This problem only occurs a few times a month. I cannot repeat the problem at will.
There may be a problem with the electronic parking brake system.
Ask your shop to remove the wheel and inspect the rear brake components. They probably will need to remove some of the brake components too to be able to inspect everything that needs to be inspected. It sounds like some interface that should be sliding is sticking.
Is it possible that is is rust buildup on the rotors? That can cause an ugly grinding noise that goes away after a few stops. Does it only happen after the vehicle has been sitting overnight?