I was riding the 426 the other day and have noticed a noise coming from my bike. It has ran fine for almost a year now for me. I also just did the 450 cam mod and that is running perfect. I always asked my friends how noisy a 4 stroke was supposed to be and they said that my bike sounded normal. Well the noise is not horrible but there. I finally put my hand on the clutch cover when it was running to see if the motor was still warm as I had taken a break for 15 min and it was cold that day. When I place my hand on the clutch cover the noise completely goes away. I have not removed the clutch cover off as I didn't have a gasket if the stocker messed up and didn't wanna end the ride early. So if anyone would just fire there bike up and listen around the clutch area and then place your hand on the clutch cover and listen for a noise to stop. I'm guessing its similar to a skidplate on my crf50. It makes a whole lot more engine noise with the skid plate on than with it off. Kinda like the clutch cover is magnifiying a noise. Let me know what you think guys and gals?