I have a 2006 CRF250R purchased used in Dec 2011. I ride occasionally and the bike has always made a whirring noise that other people notice too. The bike has made the noise for as long as I have owned it but it seems to be getting louder. I have set the valve shims twice and inspected all that you can see with the valve cover off. Nothing unusual and the cam chain tensioner works properly. Bike runs well, starts fine and has good compression. It makes the noise at idle and when you rev it up. Makes same noise with clutch lever pulled or released. Any thoughts or experience with whirring noise?