The noise I was getting was happening all the time, not only in reverse. It sounded like something was loose. It was metal on metal and it would occur at slow speeds as well as high. It sounded pretty bad but I had to drive around with it for over 1 week because I could not get an appointment to bring the car into the dealership. No permanent damage was done, and since it has been tightened I have not had a peep made from the rear end. I am pretty sure it had to do with the suspension, I will look it up for sure when I get home from work and post exactly what was done.