next time it makes the noise stick some fuel line down by the fuel pump and the block and plug in your ear, them goofy BB motors have a habit of making a scary sound from the fuel pump getting week and the rod is hammering around...
SeaFoam is the Bomb!! I run it in all my stuff now and it flat out cleans and unsticks things like it says, dont be afraid to dump two full cans into about 10 gallons of gas and run it through a car that has sat, it will straighten it right out and purr like a kitten..