2014 vstar 950 Tourer, 14,000 miles. When I'm at a complete stop and really get on the throttle at the green, I will sometimes get a clunking sound from the rear wheel. It almost feels like the belt is slipping, but that seems unlikely due to the teeth. I don't crank on it for every start, but when I do and really torque it, I get the clunk. Any ideas?