I have a 2003 yz450f, the bike has been great. I change the oil every other ride. But yesterday when i was at the track the bike ran good all day and at the end of the day on my last lap you could hear something raddling or klanking in the motor. It still runs strong and still has great compression, and the oil still looks clean. Please help I can break down 2 strokes all day but I've never broken down a 4 stroke.