I've recently developed a rear end noise. My car is muffler delete so I can only hear the noise, off throttle and I can only hear it at 20 mph or so and less. It is a clicking noise, (in the rear end, I believe) that gets faster and slower with speed, but is faster than tire speed. It is not a heavy click (or clunk) and I'm leaning towards thinking that I have a chipped or pitted bearing. Does this make sense or is their other common problems. Also is 75/90 the correct fluid for this? Thanks in advance.