My MC has a hum, a hum caused by DC offset. I had an electrician come by as a recommendation from MC to troubleshoot the amp humming. While there may be a quiet hiss coming from the speakers, I can hear some noise generated by the amp itself. That noise is allegedly caused by DC power on an AC line. DC doesn't belong on an AC line, and it baffles an electrician because it's not supposed to happen. That's not the way electricity works.
Anyway after convincing the electrician to put his multimeter on and check, we find DC on the AC line. It almost doesn't matter because we can't locate it's source. It could be anything in the whole home.
Anyway I got some new expensive high CRI LED lights. They hum loud. I swap my old dimmer switches for the LED compatible dimmer switches and it's just as loud. We tested them all for DC offset. Sure enough ALL old style and ALL new LED/CFL style dimmers all have some DC offset when tested with a multimeter. I even tested multiple brands. LED hum went away with the DC offset when I scrapped the dimmers for a standard switch. Now that I know every dimmer is a source for DC offset, I'll be pulling dimmer switches from my entire home. I yanked out 5 already, and that's just the kitchen and halls. Next stop is the listening/movie room. Anyone know of a dimmer switch guaranteed not to have a DC offset and noise? I liked having a dimmer.