92 Chevy thumping

#1

I have a 92 Silverado when you turn the key on or off it thumps under right side dash. Sounds like a vent door. What is the problem?

#2

It’s the interior vent motor. This opens the interior of the vehicle to the outside so that when the doors are closed, a pressure isn’t created to prevent the doors from closing. A common problem.

Tester