I wanted to ask the same question.
Now that my car is quiet (I fixed the exhaust)
, I can hear whinning in the back. It doesn't change on accel or decel, so I don't think it's the diff. This is a lower pitched sound that develops as soon as the car is rolling. I have also noticed that it goes away while turning to the right. I'm thinking tires, or wheel bearings. Any guesses?