Are you certain this is coming from the rear end?? Sounds a lot like front wheel bearings that are worn out. If you can get the car in the air, using all appropriate safety precautions, put in gear and have someone throttle up to indicated speed, see what you can hear (does that make sense?
) Put a large screwdriver on the diff housing and lean the big end next to your ear and listen. You should be able to isolate the noise. IF YOU CANNOT GET THE CAR SET UP SAFELY ON A LIFT, DO NOT TRY ANY OF THIS STUFF...