Had a scare yesterday, when I was heading to work, I heard a clunk when I took off. The back started to wobble up and down and side to side. Parked it back in the garage until today. I jacked up back wheel and everything was stable. Turned back wheel and felt a drag in one spot. I thought, oh no, bearing's bad. Then I noticed belt not meshing into sprocket teeth. I looked closer and found a tiny stone wedged in between teeth. Pried it out, and away I went.