Envoy with a "Door Knocker"


I have a 2002 GMC Envoy with about 99000 miles. It has started to have a lock clacking or knocking sound that happens 4 times in rapid succession every time I start the engine. It only does this once.

If it happens to not occur then it will sometime during the driving session, but again, just one episode.

It is quite loud and appears to come from the center of the dashboard under the windshield. It sounds like it’s in the passenger compartment, not in the engine room.

Any thoughts?