Peregrines have a number of calls that mean specific things, I have a list somewhere which I'll dig up and post here ....
That "squeaky door" is talking, usually one adult to another. They have a much softer tone when talking to the chicks. And a more intimate tone when they talk to each other which you don't hear much during incubation or brooding simply because its "get your butt over here and a) feed me, b) bring me food for the kids or c) relieve me!"
I'll find the more technical descriptions and post them here shortly ...
