My 2000 WR400 has a noisy motor. It knocks and hammers and it seems to have a lot of internal noise compared to my buddies bikes. The bike performs fine but the engine really has me nervous. I can hear the motor knocking quite clearly over the exhaust pipe (stock pipe). I change the oil religiously after every ride and I checked to see that oil is going to the top of the motor. What could be wrong with this bike. One note, when it was only few weeks old, it really knocked and hammered (louder than this), I took it to my dealer to find out a oil line got plugged with something and wasnt letting oil to the top of the motor. They had to replace the piston, cylinder, crank, rod, bearings etc.. under warranty. I hope I am not having a similar problem because the warranty has long expired. Please help!!