this morning when I was backing out of my driveway, on an incline, I released my ebrake and the car did not start rolling back. when I put it in reverse and started moving, I heard a pop from the back end. kind of how it would sound if your tires were frozen to the road in the winter. is a caliper bad, need to be lubed, or is the cable getting stuck? I should hopefully be putting new rotors and pads all around today but don't want to do the rear if something is wrong