I have seen belts vibrate in a GT1000 DS like you mentioned. at steady lower RPM there was a vibration, and on releasing the throttle from that RPM. It appeared that the front cam was quiet tight in the head with lots of drag. it was putting load on the belts.
Have you changed belts recently? do your cams turn freely in your heads?
Mike
Have you changed belts recently? do your cams turn freely in your heads?
Mike