New Hermod user here. Thought I’d document the problem I ran into and how I solved it for the benefit of others, as I couldn’t find a post on this exact issue when I was troubleshooting.
My Hermod was in a 4MS Pod, connected by USB to my MacBook, which was then running audio out to the audio input jacks on my Intellijel 7U case. I was getting some really nasty noise in the signal path. Both cases and my Mac were plugged into the same Furman power brick.
Through trial and error, I discovered it was the USB connection between the Hermod and MacBook introducing the noise–unplugging it would get rid of it.
As one of the cheaper solutions suggested by Loopop in his YT video on troubleshooting USB problems in audio production, I first tried a USB cable with Ferrite collars. This did not work.
So although it was pricey, I decided to try a USB isolator. I ordered the iFi iDefender (there might be cheaper ones out there, I just ordered the one that most people recommended on Amazon). It totally worked. Now the signal path is totally silent.
Thought this might be helpful for others in the future.