Your description of changing where the projector was plugged in suggests that the projector is on a different circuit than the rest of the equipment, which matches the electrician borrowing from a lighting circuit. Is that recessed lighting on a dimmer? Does the buzzing happen when the lights are turned off entirely? It's possible that the noise typically dumped onto a circuit by a dimmer could be traveling from projector to the Elite and producing the hum - and having a separate switcher in front of the wall plate might have provided a buffer (although I'm not sure exactly how).