I have an anthem MRX 700 purchased and installed in an Home Theater environment around March 2012. I love the unit great sound and great features. However, approximately 6 months ago it developed a significant audio Hum. I made no changes to the system, it just started while we were watching a movie. I have checked power, cables , grounding etc and the hum is still there. It will go away for no reason at all but it always returns. Example: on 3\/31\/19 the hum went away for no specific reason that I could determine. It returned on 4\/11\/2019. I turned the unit off and back on and the hum went away. The hum returned 6\/9\/19 and went away on 6\/19\/19 only to return about 2 months later on 8\/14 19 and it is now constant. I recently again disconnected everything, connected the unit to my neighbors power source to try and eliminate power as an issue and the hum is still there. I stripped the unit down to one speaker and disconnected all external inputs. The input I used was the internal tuner and the main center channel speaker. Hum is still there. The hum level does not change with the volume control and it is there at the same level when I mute the unit. Any ideas on what I can try next. I am thinking the problem is internal to the Anthem MRX 700 but I would like to prove that before I go down that road. Has anyone seen something like this before?