I finally got to ride my 07 YZ450. I can hear all kinds of noises as the exhaust is ridiculously quiet!!! They all sound normal to me, valvetrain, clutch, and chain. I did 3 motos, 1.2 hours, at Starwest last night; it's a very jumpy supercross style track. All I can say is this bike is absolutely perfect! It has the good traits from all my previous bikes combined, power of 03/04 YZ450, but smoother, flickability and suspension of 04 CRF 250, but much improved, turning of 06 RMZ450, but rails ruts easier, and inviting cockpit ergos of Honda CRF450. This really is the perfect bike. I can't even tell you how stoked I am!!!