I've got the same knocking @ 43k on a 99 XX. I was worried that I might have screwed up adjusting my valves at 34k or torned up the clutch assembly after several hundred 2nd gear clutch wheelies. But it sounds like this characteristic could be the norm. I like jrdxx's idea of the back lash on the counterbalancers. Maybe I'll try adjusting them again
g1ray2001 (George)