This evening I was riding my 1998 YZ400 and started to hear an intermittent knocking noise. It is not a piston knock too intermittent. Put it in the garage and took covers off and found the decompression lever was stuck open. So I started it up again to see if that had anything to do with it and noise still there. Shut it off right away. Bike starts just as easy as always. Shifts fine too. Not sure wear to start. Going to pull oil filter to look for trash. Oil was full and clean too. Thinking possible cam chain or valve adjustment or even chain tensioner. Just looking for alittle direction. Thanks.