I think that he has imaginary friends that hang out by the door. He tends to spend a lot of time there just jabbering and pointing. His nonsensical babblings have gotten very frequent as of late. In frustration or anger, instead of a terribly obnoxious scream, he actually now yells gibberish. It's an improvement from the scream.

I have no idea why he decides to bash his head against the door in this video. Perhaps his "friends" told him to do it.