Is he "doing anything" while he's making this noise? Like against a perch, a toy, etc.? Because that really does sound like a cockatiel having some special "alone time", either by himself or with a mate.
Notice the position of the tail in that video. "He" is getting it on with a perch! And doing it in a way that's more like a girl than a boy. I can't see the bird's head well enough to tell what sex it is. I think I can see a little glimpse of bright yellow though. If he has a bright yellow face then he really is a boy.
All my posts and all photos belonging to me are copyrighted by me. All rights reserved.