My belt in the engins slips only when i put the car in reverse and get ready to leave a spot or garage. It doesnt do it everytime, just at the most inopportune times (like people hangin around my car). Im going to dealership on monday but if it wont do it, they probably wont do anything about it...is there a way to tighten a tensioner anywhere or something to tighten it up if dealer wont fix?