Everyone is comin at this from the wrong angle, the facts are that it nocks above 8000 rpm especialy on the freeway and up hill so the throttle is open and the motor undr heavy load. Carnt be rear cush or cam chain whip cuz the load is constant,but, we have jetting that seems wrong and previous cam chain tensioner problems,so it could be related to the mixture or it could be other worn parts related to the cam drive chain, thats if the sound is in the TOP of the motor,so this is where i would start,but, i would always go back to a good set up and then work forward again.