Mine is an ´88 GL 1500/6 with about 54k miles; it, too - makes a shaft output noise...but only when I have a rider with me and we go uphill. According to the ´88 GL 1500 shop manual...a copy of which I bought from my local Honda dealer...such a noise could be a sign the output shaft bearing is about to go out. So, guessing that repair would about clear out my savings...I baby it and don´t put too much torque to the drive train.