I've ridden the bike on less than 20 occasions, the frame hasn't hit anything, the bike hasn't hit anything, I've not done anything more than try backhopping on flat ground. If the frame is cracked then it was bought cracked, new, from SuperCycles. I'll look for the freewheel info and try tightening the pedals, thanks. Edit: I worked out how to tighten the freewheel, tightened it, and now the problem is gone. Thanks very much.