I have an '03 predator and just had a wiseco piston kit put in (stock size) and the builder suggested replacing the valves which I did. I have about two hours of easy riding on the motor now and it seems to have alot of power. My concern is that when I back off the throttle, there is a clanking noise in the motor and it continues while in idle and after about 30 seconds of idling, it goes away. If I rev it, it comes back and does the same. Any ideas??