I'm frustrated with this. I've had this happen before a while back and it happened again today. I have 2012 rmz250 that I have a somewhat new yoshimura exhaust on and later in the day at some point the thing just becomes super loud all the sudden. What could be the cause besides exhaust leaks or packing? Would boiling gas cause or the valves? Or is it because the engine has gotten really hot I just cannot figure this out. I have replaced the exhaust gasket at the cylinder head. I have completely taken the exhaust off and re fitted it. It does not do this at the beginning of my ride. Maybe I'm running too rich or something I just don't get it. Any help would be welcomed.