The only thing I can add to this thread that I moved to a new house I got a hiss sound coming from twetter and the old house got it too. I think maybe is normal We don't know exactly what we cause them RFI some error on ground. Some kind of electric static we don't know really I have been this road since lot of time a little trick I can add is that the more time you keep your ear and brain on this better will be cause really there is not solution really and it's not a problem since in my case at least that doesn't bother me to produce music.I don't know in your cases maybe it's louder than me but. At least I can say I have a virus b electribe krk rokit 6 focusrite 2i4 and a computer pc changed the standard cables to Roland gold cables same "problem" I mean the ear becomes more sensitive so you will be hearing more of that sound... I think it have its parte psicolgicaly and changed pc to my mother pc with Mac same problem changed from house as a said same problem... connected directed to powered speakers same "problem"... with both machines. connecting only the interface with the pc and hearing only pc sound same but less louder ... I don't know,, we don't know what can be...

My guess. When I have the turntables technics mk2 and connected by XLR cables maybe don't have that sound I DONT remember maybe my ear was less sensitive..

And finally my guess forget the sound if you can find the cause really because can be a lot of things I can se hundreds

The best for you smoke some w33d and get relax