I noticed a thread a couple days ago... more on engine noise. My used 06 yz450 bothered me so much with the noise, I tore it down. New piston, rings, valves were at the tight end of good so I shimmed them back up to the fat end. Bottom end was tight. After putting it back together, it starts faster and runs just as good as ever. But it's making more of the tapping noise now at idle than ever. Goes away off idle. So the guy who said the valves being shimmed would make more noise, I hope he was right. I don't have the stomach for such a loud racket coming from my engine. I've been around this stuff for decades and I can't believe yamaha let the engine go out the door making that racket. I love the bike though.