I am diagnosing an '06 YZ450F this week (not my own), and when the bike is warmed up it has a nasty loud rattle coming from the top end (seems to be more on the right side of the motor when I listen with a screwdriver). Can this just be the valves out of adjustment? Loose chain? I thought about super loose crank bearings, but I've never heard any THAT loud, plus I could hear that those were rolling smoothly. I'll be pulling the top end apart this week most likely - suggestions on what to look for?