What kind of head shaking, is it a nervous type, or is it in response to a sound? I know some of my chicks will shake like they have something in their ears if you hum loudly at them. Is there a computer near by? Could the sounds of the HD or monitor be disturbing them? Like those really annoying high pitched sounds that come from them that a lot of older people can't hear, but drives undamaged youth ears insane.