I have a 2003 c5 and I hear a roar in the rr of the car. When driving since I bought the car this summer I have heard tire sounds humming at hwy speeds. I just thought it was the pilot sport run flats. As time has gone by the sound seems to be getting louder each month. The car has 115,000 miles on it and I think it might be bearings now. How often do bearings need to be replaced and should I do both sides at ounce?