Having noise issues on your external USB audio interface when connected to a desktop PC and powered studio monitors? Chances are you’re having issues with your grounding… Make sure you are using balanced cables, meaning three wires (two phases + ground) to connect your speakers to the output of your interface.
I recently spent quite a few hours chasing down an extremely annoying crackling hum on my audio setup because of that. No ground loop, all devices connected to the same circuit, I even hooked everything up to an online UPS so I get perfect sine voltage but to no avail. When connected to my main workstation there was a noticeable and extremely annoying background noise on my monitors that wasn’t there when I plugged the Focusrite Scarlett 2i2 into my notebook or mobile phone via an USB OTG adapter. Heck, it wasn’t even there when I plugged it into an HP Z600 workstation that is sitting right beside my main computer, all connected to the same UPS, ethernet switches and whatnot…
Turns out I used unbalanced cables from the Scarlett to the monitors and apparently the MSI X99S mainboard (or maybe the power supply?) in my primary desktop computer has for some reason quite a bit of noise on the ground of the USB bus. Or something like that – I didn’t bother to get an oscilloscope to verify.
Swapping the cables from TS to proper TRS (tip-sleeve “mono” to tip-ring-sleeve “stereo” aka balanced) fixed it and everything sounds perfect, no matter what computer the interface is connected to.