Interior thumping noise left rear

[400E]

Hello,
First post on this forum - I attempted to search on this but didn't find anything.

I have a 2002 Explorer with 50k miles which has rear HVAC controls. For about a week I have been hearing a rhythmic thumping sound which sounds like it's coming from the inside of the panel which has the door lock switch for the 3rd row seat passengers. Sounds to me like a solenoid repeatedly firing.

It seemed initially to go away when I turned off the rear AC, but now it still does it regardless if the rear AC is on or off or the whole ACC system is on or off. Hitting the door lock switch doesn't affect the noise.

Thanks in advance,
Steve
Omaha, NE