I am not sure this will help. But it seems you are trying to cure the symptoms and not the reason they scream. "Food" I have an imprinted male Harris Hawk in his fourth season. And he hasn't screamed in years. The first few months were pure hell though. For Diablo all it took was hunt, hunt and more hunting. Once he was consistent hunting he just up and shut up. He still talks a lot as I think all HH are prone to do. But it more of a grumble under their breath and definitely not a scream. I have to be paying attention to even notice he's talking. But then again Diablo is a weird bird so no guarantees. First months I had to tell my neighbor that he would grow out of the screaming after he started hunting. Boy I lucked out on that one.