I've got a 97 A6 and I had a noise that sounded to me like a bad wheel bearing, I replaced one side and the noise became louder. I figured the other side was bad so I replaced the other side wheel bearing, now that both rear wheel bearings have been replaced the noise is still there. if I'm driving in a strait line I hear this mystery noise however if I pass another car or take a turn the noise will disappear. any suggestions as to what it could be???