I know the vibrations this thread talks about. I got a different vibration and just wanted to throw this out. When I ride my bike like a John Deer tractor at a steady 2,500 rpm in 1st or 2nd gear, I feel a grinding sensation in the footpegs. I know nothing is grinding because the bike is so un-stressed at this moment. But grinding is the sensation. Probably some bad harmony from the muffler or the drive chain slacking out it some weird way on the plastic guide.