Today I visited Blue Ridge Parkway in my 08 Surburban 1500. I drove about 50 miles before getting off. After we left the parkway, I noticed the steering wheel vibrating and a low audible sound coming from the wheels. It sounded like a big MAC Truck winding down its gears to a stop. The brakes seemed to continue to be working during this. I did not ride the brakes during this trip and was supprised by the virbrating stearing wheel. Once off the Parkway and after driving for a few minutes, the noise and vibration was gone. Could this be caused by brake fade? Anything to be concerned about this?