[KC10Chief]

Yup. After watching your videos, that is most definitely your problem. That metal plate is rotated 180 degrees in the wrong direction. Look at the sides of your square hole. You'll see rectangular holes on each side. Those are the ducts leading to your roof vents! Since your metal plate is turned around the wrong way, it's essentially cavitating when you close that plastic diverter. The larger hole in the AC itself is the intake and the smaller one is the exhaust. The diverter should be on the same side as the small hole. When you close that, you're actually sucking air in through the vents for a bit but it has nowhere to go. Anyways, it's a super simple fix. Unbolt those four bolts on the metal plate, rotate 180 degrees being careful not to tear up your wiring, and bolt it back down. Problem solved!