Ahhhhhhhhhh.................. Welcome to the world of the stainless steel exhaust on the Foreman 400. They ALL do that eventually. Honda went to stainless stell because so many mufflers were rusting out and eliminated the rust problem but made another. The rear baffle comes loose in em. If you can find someone to weld the back of the muffler you can cut into it and remove the old one , then weld the back of the muffler back on. I will still be a touch louder, just without the rattle. It will also more than likely start backfiring when you let off the throttle once in a while. Prob not that often but that is a classic symptom that accompanies a loose baffle. I have had mine backfire 5 times on a 20 mile ride and a few weeks later backfire once on an 80 mile ride, so it will not always do it.