I guess I haven't experienced screaming for what seems like no reason. She contact calls, and gives an alarm screech when someone comes over. Sometimes she screeches out of joy, but I don't have a problem with that. My BC did that, too. She also screeches about anything I bring into this room that isn't normally in here, including the vacuum and broom every day. But, that is her being territorial. I just ignore that, or say, "It's alright", which seems to calm her down some.
Pete will scream when he is upset about something, and that something might be me in the kitchen making dinner. And he can see me while I'm in there. When he does that, I totally ignore him until he stops. I think he still has anxiety issues though about being rehomed. He is the one who worries a lot whenever I have to leave for any reason. And if I'm gone for more than a couple of hours, he will scream when I return, too (not a greeting, but screaming out his anxiety over my being gone). I think eventually he will come to realize that I'm always coming back, and that he's not going to another new home.