low rpm/idle knock

[joey11]

I'm just getting my 06 250 set up and the engine seems to be knocking while at it's lowest rpm/idle and at the very first crack of the throttle. It goes away if I pull the clutch in and it revs and rides great with one exception. This knock occurs while the engine is at idle on downhills or hard braking. It may just be the engine, but it does not sound right. I am going to change the tranny oil to Rotella today and try it again. I've had at least 10 seasoned riders (not mechanics) look at it and they are all dumbfounded. Comments range from "I've never heard one do that before." to "I don't know if it's an engine problem or a clutch problem." Any ideas fellas. Thanks in advance.