Originally Posted by LGERIC
Fast forward to this week and I have a hum returning and I don't know why.
Things don't just magically start happening, something in your system has changed.
You need to start from a basic wiring topology.
Remove all wires and antennas from the AVR, including USB and remove triggers. EVERYTHING!
All you want is the power cord.
Connect the subwoofer output directly to the inuke.
Any hum? Then one of those two devices (or the wiring between them) is the problem.
If no. Step 3)
Connect the other inuke with a Y-Spliter.
Any hum? Then the Y-Spliter is the problem, or the second inuke. Revert to Step 2 and swap the inukes.
If no. Step 4)
Remove the Y-Spliter. Connect the inukes with the miniDSP.
If still all good. Step 5)
Add each speaker wire to the AVR, one at a time.
If still all good. Step 6)
Add all optional triggers and antennas
If still all good. Step 7)
Add each HDMI or RCA or USB or other metal cable ONE at a time. Until the problem connection is found.
-Make sure power wires are not running parallel to speaker wires or interconnects. Perpendicular is ok.
-Do NOT coil ANY wires.
-Keep wires as short as possible.
Most ground loops are caused by one or more components leaking electrons into the chassis and/or grounding wires, and this power finding its way into the signal ground or signal hot (and then amplified to audible levels.)
USB and Coax wires are notorious for this.
Cheap switch mode power supplies can leak enough RF or electrons into the chassis or house-ground to cause this. Also LED lights, dimmers, and motors/fans/pumps.
Even using different dedicated circuit breakers can cause this, due to voltage differences between the ground pins, cause by corrosion and line length. Especially OLD wiring, not so much new wiring.
Unfortunately ground pins and ground wires are required by code, for electrical safety.
In the event of a hot wire or system fault coming in contact with the chassis, without this pin, anyone touching the rack or device could get electrocuted and/or cause other inter-connected devices to be fried (audio & data etc).
This power would flow back to the service panel, across the ground-neutral bonding jumper, back to the pole transformer, and back down the hot wire, tripping the circuit breaker at full rated line-current (say 15a or whatever).
Ideally there would only be a single ground conductor in an audio system, rather than each device having a parallel or star connection.
Each device would be grounded to each other in a straight path back to the wallsocket ground pin, with all other ground pins lifted.
What works best for audio, doesn't work for electrical code compliance; at least in residential structures.
Some exceptions can be made in radio broadcast rigs and professional recording studios, and other such stuff.
If the hum was bad enough, and you had GFCI's on all circuits, I'd imagine the one causing the problem might be sufficient to trip the GFCI breaker. I think those have a 15mA cut-off...