E.O.
Oh, good -- reading the other responses, I'm comforted, because at about 9mo-12mo, my baby did the same thing. It started to feel like more than just a stage after about 2 months of it, and it wasn't cool for her to do it when we were out shopping, or visiting, so her daddy and I just began to whisper to her, "We talk in quiet voices" and so on. We really worked on regulating our own volume, too. We never yell at each other or anything, but when she would get wound up like that (and it was most of the time) we'd exaggerate "gentle voice". She kicked the screaming habit about 1 or 2 months ago, and it's been a big relief.