Air Conditioning Door sound

[J_G]

Hey, this past weekend my car started making this repetitive knocking sound whenever I turn on my Air Conditioner and I have it set to recirculate the air inside. It sounds like some electronic mechanism is stuck and malfunctioning. It sounds like a knock, knock, knock, knock coming from inside the dash and won't stop. Only when the air recirculation button is lit, this occurs. If I press the "air outside into cabin" button, the sound goes away. So I'm guessing whenever the door is CLOSED inside the ducts, it doesnt want to shut. I'm not sure what exactly that part is. Anyone ever have a problem with this?

I noticed when I turn the car off, some electronic sound happens from within the dash, I'm guessing again it's that door closing. I can also post a video with the sound tomorrow when I get some time if that helps. Thanks.