I checked the CB gear and valves/timingchain and nothing seems to be wrong. My 99 yz400 makes a rattling sound when cruising at maybe 1/4 throttle. It only does it in gear. The only thing that I did change before this started was oils. I have been yamlube 4R since I bought it used in Oct. I decide on this last oil change to switch to Mobile 1 sythetic. Could the change in oil just brought out a new noise. Once again the noise is pretty loud and sounds like I would imagine the timing chain to sound like if it was slapping. Thanks for any ideas. Khris ------------------ When in doubt, GAS IT!