I have a 2000 cadillac DeVille, recently I've noticed that when coming to a hard stop I am hearing knocking noises, sounds like it's coming from the rear wheel. I have no idea what this noise is and was wondering if any one knew before I take it to the shop. It happens when I am slowing down and hear it a little more as I am coming to a complete stop. Any ideas? It is not coming from the engine