I think this may be a breed trait.. or maybe we both got "lucky", haha. My SG Dorking, Opal, is extremely noisy too, especially when she sees people.
I find it kind of endearing most of the time even though she has perhaps one of the worst voices of any of my girls- I agree that I would call it more of a scream than clucking. It's possible they're a defensive breed- Opal is nice, but she's always right there, keeping an eye on me when I'm gathering eggs or working in the yard and she goes after every sparrow and squirrel that finds its way into the run. In her case at least, I assumed the screaming was just another part of that.
I don't know that it will get any better when she lays, however. Mine has been laying for a month or so now and her level of noise is about the same.