Cockatiel squaks when preening between his upper wings.

by Rebecca L.
(Sterling, Alaska)

I have a cockatiel that appears otherwise healthy except for something he has been doing for about a month or so. He turns his head around to the back and preens between the top of his wings. While he does this though he squaks very loudly and visciously attacks himself in that spot. He acts as though something is in there that is bothering him.I thought it might be just a passing thing but it's not. This happens many, many times a day. It's driving him and myself crazy. What is it and what can I do to help?