Power Port seems to hum

I have recently had a PS Audio Power Port installed in my wall by an electrician and after a couple of weeks now I'm noticing a slight hum from the wall where the duplex outlet power port is installed. What is new about my system is that I have a P500 Power Plant now connected to the power port via a PS Audio power cord as opposed to the Power cord from power port in wall connected to ultimate outlet. The only thing I can think of is that perhaps the P500 is drawing alot more current than the passive ultimate outlet but this should in theory not make my power port outlet hum. Any suggestions or help would be appreciated. I should mention that I live in a house with a family living above me and below me therefor taxing the ac of the house and an electrician said that a dedicated line would be next to impossible if not extremely difficult and expensive. One last thing I should note is that the hum is slight and only noticable if I put my ear right up to the power port socket. Thanks Mitch