Ive always noticed since day one of having my motor , that it has a slight rattle. it sounds like its either in the upper part of the motor (jug) or down in the bottom , its hard to tell , but it is there! as far as performance , I havent had any problems it seems to run fine. at top end you dont hear it , at mid range ,yeah its there , at idle you know its there! the motor was sold as a "80cc". Ive rode with Hookwormrider1 last weekend and his motor seems to sound a lot tighter than mine. any solutions or just the nature of the beast.