Audible High Pitched Hum... Advice Needed

Why don’t you add an AC switch between your power source and the component/s that are causing the issue when not in use?

Those noise issues can be difficult to solve and a process of elimination is the only sure way to pinpoint it. Not the ideal solution but have you tried an inexpensive inline filter? These worked for me when I had a similar issue with a secondary system years ago. The buzz was of the type you described.  I was actually surprised they worked so well considering the cheap price.  If they don't work for you just send them back. Use them on the input side. I bought a few from Amazon.

MEIRIYFA Car Stereo Audio Filter Suppressor, Car Amplifier Noise Filter Isolation 2RCA Male to Female for Car Power Amplifier, Studio Recording Equipment

What about a product like this? This is just going to add up as it will double my interconnects. I wonder if introducing this between the XMC-1 and my I-5 will solve the issue. I suppose I can always start with 1 and see how it goes.

https://www.markertek.com/product/il-stereo-19/sescom-il-stereo-19-pro-audio-hum-eliminator-2-channel-rca-hifi-style-stereo-isolator-transformer-coupler?gad_source=1&gclid=Cj0KCQjwwMqvBhCtARIsAIXsZpY6JsUWaeLGJ80YbAEqhtm1V3b-iiaN8O9z1LKseD2fyeXrNtD_dcgaAhXvEALw_wcB

Here's another more expensive option - not sure of the difference.

https://www.fullcompass.com/prod/036365-jensen-transformers-ci-2rr-stereo-2-channel-audio-input-isolator?gad_source=1&gclid=Cj0KCQjwwMqvBhCtARIsAIXsZpaACb3K2voGDtniND9HPr_w18_TfFSMtcyNPJMhLVeoPcEuTRLgJjUaAmoKEALw_wcB

I don't see why that would not work.  Seems like better quality and probably does the same thing but I'd see if Amazon has one just because of the easy returns in case it doesn't solve your problem.

So you are aware, HDMI is notoriously noisy and prone to causing ground loops, ESPECIALLY from PC's.  PC's are just prone to ground loops in general but HDMI seems to also be bad.

Any coaxial cables coming into the HT can also be suspect.  The test in all cases is to turn on all devices but disconnect the suspected cause of the humm. When it vanishes you have found the problem.  It's of course not usually just 1 item sometimes it's two.  That is, sometimes it's 2 different devices which cause the humm.

The ideal and relatively inexpensive solution, whether your problem is HDMI or coaxial is a ground loop isolator.  In the case of a laptop, another test is of course pulling the power adaptor out of the wall, but that's not often very useful except as a proof of concept. 

In my case, my phono pre and my streamer/dac when plugged into my preamp, seem to amplify noise coming from my PC. If both of those units are disconnected from my integrated - PC is dead silent through my AVR and TV. It sounds like I should just try a ground loop isolator and see if that helps.

@ajnackman Why do you have the streamer grounded to the same place as the phono? That's a recipe for a ground loop. Won't the streamer work without grounding it?

I've tried it both using a common ground location and keeping the streamer ungrounded without any audible difference or behavior to the hum. The turntable a phonopre require grounding together or I get noise issues.

So I purchased an ART DTI dual transformer isolator to try out and installed it between my AVR and my integrated amp - the reduction in the hum is impressive. If you stand right next to the speakers you can still hear it - and I can hear some of my other input leaking through at very low volume if I have my Dac playing. Overall very impressed for 80 bucks. 

ajnackman OP  Good to hear that it worked.  The one I recommended probably would have done the same thing with no noticeable audio degradation for $8.90 each. You could have gotten 8 or 9 for the same price as the ART DTI.  One for every input!

Did you check everything concerning your cable box? Have the cable company check it making sure it is grounded correctly. 

Don't have a cable box - I stream everything from my TV connected via ethernet. The hum eliminator definitely helped in my case.