I just bought a used 08 yz450f. The guy I bought it from said it had less than 20 hours on it. I was just wondering if any of you could let me know if there are any known problems I should be aware of with these bike. Like the engine makes alot of noises,is this normal,or should I be concerned? This is my first 4 stroke dirt bike so I'm obviously new to them,any comments or advice would be greatly appreciated.