Motorcycle Repair: engine noise, piston pin, auto mechanic

Question
I have an engine noise most noticable in high gear between 60 and 70 MPH while under load,if I let off throttle it goes away.It is a constant knocking noise that sounds like piston pin knock in car motor.I am a retired auto mechanic
and this noise bothers me but don't know if this is normal for Air cooled motors.The bike is 2002 RD KING with 13500 miles. I also can hear noise as I go thru gears at mid RPM.Thanks

Answer
Noises on here are hard to determine, due to the fact I cant hear them. You are probably hearing lifter noise. Since the lifters are outside the motor you can hear them ticking. right now I wouldnt worry, but if the noise get louder or the bike starts running bad then you will have to do some investagating, but tearing the motor down from the top end.
Good luck and happy riding
Mike