was running my shee today. and when i stopped and let it idle, it started to make a weird sound. and would blow out a hard blow of air. not for sure what this is.. had banshee's before and my last one did this but i cant remember what it was.. been 5 yrs ago.. any comments appreciated... is it detnating or carbs out of sync or what.. im lost.. only does during lower rpms... thanks a tone.. ] its bone stock on stock bore... thanks