Quick topic. So everyone knows, there are 2 possible types of ground loops a DAC can be subject to. Still.
The first is the normal, audible hum caused by a ground loop. This can happen when the source is on a different AC branch circuit for instance. It's exactly like every other ground loop problem most of us are familiar with. Just like them, this requires metal to metal signal transmission. In my mind it's very disappointing that this even happens anymore since USB isolator chips, and coax S/PDIF transformers are plentiful and cheap. My Mytek Brooklyn absolutely shows this problem when I run a long USB cable to my PC, something I only do for audio testing. Fixed it by switching to a laptop.
The other type of ground loop issue is in the digital domain and evidences itself as excess jitter sidebands. I have seen measurements for this, I think in Stereophile. Again, same exact cause but we don't hear it the same way. There's no audible humm.
Even a cheap, hospital grade USB isolator would fix either issue, but in the case of the Mytek, these won't work. I haevn't tried an iFi with it's own additional power supply though.
If you have Ethernet you should not have any ground loop at all. Because Ethernet is meant for long runs, with equipment at various ground potentials to begin with, it is galvanically isolated at each end. However! A 4kV hospital grade isolator is inexpensive and often used for lightning protection. If you try one and it helps youyr audio quality do let me know.
