I have Denon AVR3805 and hooked it up with Polkaudio speakers (Monitor 60, monitor 30, CSi1 and PSW12). I just noticed the hum noise coming out from speakers, especially the front and rear speakers. I turn off all other units but the hum noise is still there with AVR3805 on. The hum sound can be heard when I turn on the AVR3805 and turn the volume all the way down to 0. Any suggestion to get rid of this hum noise.