Internal rattle from exhaust near engine compartment.
Air Gap Pipe Failure
Air gap internals fail due to internal corrosion.
Inspect air gap pipe by tapping with a rubber mallet while listening for internal rattle. Complete inspection by removing pipe and inspecting internals. Replace if internal pipe is dislodged or rusted through. Note: Air gap pipe is an emissions component. Always replace with air gap pipe or converter may not light off under certain conditions.