Everything including projector is plugged into the APC. Only exception might be a Unifi wifi access point POE injector sharing the duplex AC outlet the APC is plugged into. Ethernet cable from Poe injector plugged into switch in rack.

I have tried lifting ground on individual components (not all at once and just audio components and projector) with no luck. FWIW you can also get rid of the hum by unplugging all HDMI cables from the Marantz. Each individual HDMI cable, when plugged into the AVR individually, produces a smaller amount of hum so I couldn't seem to isolate it to a certain path. When they're all plugged in is when it was the loudest.

One last thing I would like to mention that was strange, is that when troubleshooting and looking at at the APC, I started off by bypassing it and plugged an extension cord straight into an outlet in a different room and for some reason the hum got like 10x louder. Tried it back in the dedicated outlet for the rack and it cleared up completely. Wonder what was up with that other circuit and if it's related at all to to my problem.

Thanks for your responses.