Apache definitely doesn't scream. At times he talks though. He didn't start talking until I got back from my trip and had been tossed food to for a week. My experience is that as you establish the idea that they are working for their food, the quieter they get. Hunting, RP's, etc...encourage quietness. Giving them free handouts (tossing them food) encourages noise. They might get vocal when you drop their weight initially, but most accipiters quiet down as you establish their work ethic and they are hunting hard.