Was out riding last month in some serious heat and boiled the coolant in some slower single track stuff. Shut the bike off right away and let it cool down. Rode it multiple times since then without problem but the other day I noticed that while idling when I put it in neutral and let off the clutch a humming somewhat grinding noise appears. And it only appears when i let up off the clutch not while i got the lever pulled- almost like its engaging but not moving???? This is definately new. It never made this kind of noise before. Does this have something to do with the overheating incident or is my clutch staring to go? Its an '04 wr450 and has only been ridden half of last year and only some of this year. I don't really abuse the clutch either.