Brake problem
 

BRAKE PROBLEM backing up makes a rubbing howling problem . Took it too my mechanic and he made it a little better but still there . It's on the back , does the salt in winter get on the slides of the calipers and corrode them on the metal of the brakes ?? Will never seize lub stop the problem ?? Only when backing up and then again every time I re-back up

The rear brakes have a combo drum/disk to allow a shoe brake brake for the emergency brake. Perhaps the shoes are binding. When backing up apply the emergency brake and determine if the noise changes.