[jsinton]

Get a piece of plastic tube and stick it in your ear. Use it like a stethescope and track down the location of the sound. I'd say you just got something spinning around and hitting a piece of plastic, etc.

A long screwdriver can also be used like a stethescope to locate things like noisy valves, etc inside the engine. Just stick one end on the motor, and one end in your ear. You'd be amazed how clearly you can hear valves.