@chedwin I wasn’t even thinking of the HDMI cable since the noise is ultimately emanating via the sub amp. It may be mostly mitigated in the AV section (digital), but the analog section is definitely having problems with it. Also makes me wonder if there’s enough EMI to pass through to the analog section, then what is the analog ground referenced to and why doesn’t it squelch the interference? Perhaps the best thing to do is to start measuring between different grounds to see if there are any potential differences (the reason I asked about diagnostic equipment). I would also check inside the PC for misaligned ground screws and check from the case to the ground wire on the power cable, since the case “should” be a good Faraday cage, unless it has a window on the side. Maybe check to see if the GPU heatsink is grounded.
The ferrite beads you ordered should be put on the signal wires close to the output connectors.
That’s enough for now.