I have a friend with an '06 450. His bike has about 65-70 hours on it similar to mine. It just started making a loud noise while running. No metal in the oil and the bike runs just as it did before. The noise came on very quickly. The noise is a loud rythmic one that does not sound to me like the knock of a bad crank. It is the same mechanical clanking that my 450 makes (and always has just as all of them do) just magnified by atleast 3X. It is a high pitch tick...tick. I know that all of these motors have a lot of noise while running. This bike has just developed a much higher volume of the same noise. It is to the point that it is obvious that something has to be done. The valves have been checked and they are perfect. It is time to dig in farther. What should be expected and what should be looked for?