Ozzuneoj wrote:

Ground loop isolators shouldn't usually be needed for most setups, even old noisy sound cards. I'd test the card in another system first. If it does it there too, test it on a board outside a case (no metal contact). If it still does it, it may be defective or need cleaning.

I did just that yesterday afternoon and it's the same. What do you mean by "cleaning" the card? It looks clean 😀