My buddies 01 250f has started to make a wrrr-wrrr sounding noise. It seems to be coming from the cam chain side of the engine. It starts as the bike gets hot anf gets louder the hotter the bike is. The cam chain tenioner is working, nothing seems to be rubbing when peering down the cam chain side. The noise isnt effected by the clutch but is effected by rpm. Any Ideas?