Ground loop on 1 PC with 2 sound devices?

I have been experiencing audio hum + hiss + screeching when both sound devices in my workstation are connected to the same stereo line mixer and the levels on the mixer are not equal. Unplugging either sound device or equalizing the levels makes this completely disappear. As of now I am currently using this setup by having the two mixer channels my workstation uses equalized to eliminate the background noise. This is not ideal though because it defeats the purpose of using the mixer in the first place. All other audio devices I plug into the mixer do not cause any noise, it only happens when both sources from the workstation are connected.

My audio setup is as follows:

Realtek ALC1150 onboard audio chipset (Debian 9.4 with 4.14 realtime kernel as hypervisor)
NVIDIA GTX 1070 HDMI audio to monitor with built in DAC. (Windows 10 VM)

Thinkpad T420s

All 3 sound devices are connected to a stereo mixer which then goes out to my speakers and/or headphones. Everything is powered by a single power strip. I tried separating the monitor, mixer, and workstation by running extension cables to other rooms, as I expected it amplified the effect.

Since it does not sound like your average ground loop hum, (its more screeching and hissing patterns that correspond with the load of the workstation than a constant background hum) would adding inline audio isolation transformers between the monitor and mixer be able to eliminate the noise? I would like to just salvage transformers from something else but am not sure what type is suitable for this application. If I don’t have anything laying around that I could hack up would someone also point me to one that will not distort the audio and is also not overpriced snake oil?

I’m no expert in audio issues but have had some experience in troubleshooting ground loop short issues with some USB devices. Have you tried a simple ground loop isolator? They are < $10 on amazon.

I have looked for some but most have reviews saying they noticeably effect the frequency response. I may just have to try it for myself though as I have learned not to trust reviews from online retailer websites. I think I will go to a few local shops on my upcoming day off of work and see if I can find one locally, that way it would be easy/fast to return if it does not solve my problem.

I have recorded a sample of the noise at its worst (when one channel is at minimum volume and the other is at maximum)

I ended up buying this, it completely eliminated the noise, it colors the audio a bit (noticeably warmer) but I suppose I can deal with it as I am using it for a gaming VM.

the only other thing to check out is if you have a mic on that you are not thinking about. feedback can be fun.