Sadly the wiki hasn't updated to 0.9 and it seems this was added in 0.9, so I have some questions. Banging on which door? And what happens when I barricade the door(I'm guessing the hidden door)?
There is a walk-in freezer in the Alpha base basement. You can’t miss it, it’s facing you when you finish coming down the stairs and turn left. I think by default it’s sort-of covered by those mobile curtains. You can’t open the freezer door, and those curtains are about as much as its allowed to cover it.
If you stay too long in the basement (I’m not sure of the exact trigger), you will hear something banging on the door of the freezer. At least one youtuber had a slow-mo view that shows the door is shaking on its hinges with every bang.
Additionally, if you try to place a heavy object against the door, nail anything across it, or use build tool to wall the door in, the banging will begin the moment you walk away, and will keep going until the object gets toppled or thrown away from the door. Built walls get destroyed eventually.