I have definitively pinned down the sound of the screaming noise: baby great-horned owls. I saw one perched atop a telephone pole tonight, ear tufts and all, with the sound of another also shrieking in the distance, which I later also spotted. They may be from the same nest, spread across several acres for feeding over a wider range. They look almost full-size, but are still demanding parental attention, so they're probably not good at hunting yet. They are somehow adorable, sitting up there screaming. So we not only have great-horned owls in the area, they are breeding well enough to fledge chicks. :D 3q3q3q!!!