My 1988 elite is suddenly making a high pitched whirring sound that seems to be coming from the rear...no noise at idle, only when the rear wheel is spinning. The faster the spin the lounder the sound, even when on the kickstand. Perhaps some loss of power but I am afraid to drive it to find out. Transmission? Rear wheel? Bearings? Exhaust system? What is the likely reason for the noise...hopefully an easy and inexpensive fix. Thanks