DIAGNOSIS A loose or damaged cooling fan shroud or a loose recoil starter assembly is vibrating against the flywheel cover.
FIX Tighten the fan shroud and recoil assembly screws.
1. Disconnect the spark plug wire for safety.
2. Remove the two main plastic side panels.
3. Locate the black plastic fan shroud around the flywheel. Check all its mounting screws and tighten any that are loose.
4. Check the three bolts holding the recoil starter assembly to the engine block and tighten them.
IF THAT DIDN'T WORK Inspect the metal muffler shield. The heat shield around the muffler can develop cracks and rattle—secure it with a large hose clamp.
HEADS UP Do not ignore this. A loose part can break and cause catastrophic engine damage from overheating or physical interference.