Strange noise coming from engine

[krisrtch]

I have a 06 CR250R. This past Saturday I was racing and when I would get on it , it started to to make a clanking noise. It only did it in third gear. When I would wind it out in first and second everything sounded great. but as soon as I dropped it to 3rd sounded like the chain was clanking against something. then during the 2nd moto it was gone. I looked at the case saver and it did not apear to be damaged from the chain. Then I went out Sunday and it started doing it again. but not that bad. Main time it did it was coming up to the jump face. The tranny fluid is a proper level as I check before every ride. Any one have any ideas what might be causing this. I have the next 3 weeks off before my next race and would like to remedy this before I completely destroy something.
Thanks in Advance
Kris

[R4ever]

is your chain tight? is your pipe and silencer bouncing around? could it be piston slap?

[krisrtch]

It was the Chain. I changed out the chain and sprockets last night and sound is gone. it was the stock chain about 3 months old.