one day i was rideing around at my little track at my house i was in second gear the whole way around not reving much at all. aFTER a few laps i herd a bad noise like a gear in my motor wat picking somthing metal up and throwing it around the. the sound only happen when im moving and hit the gas. i took apart both sides of the motor and there were no damages or mettaL shavings. i even checked my under my valve conver there are no qlues of any thing bad.the motor is very clean. i even looked around wit a tiny camra were my eyes canot see without takein to much apart . please help every thing works fine just mAKES a quick grinding noise i dont think its my chain any ideas wat it could be?