Input ground loop hum only when p10 cables or XLR without phantom power are connected

Yeah, I've tried that, when I disconnect the power cord the hum vanishes...But if the problem is in the USB cable, why does the output sound perfect when there's nothing plugged into the Scarlett inputs? (I've tried switching the USB cable from the interface, and problem persists...haven't tried the galvanic isolation adapter)

TRS cables. Sorry, that's what they called them here in Brasil, forgot to translate

No preamp, just a Scarlett connected via USB cables into my notebook. The cables causing the problems are the one on the Scarlett inputs, that I use whem I connect my guitar or bass with TRS cables or a mic with XLR ones...I've read that post, but what intrigues me is that the interference/hum only appears when I'm recording, when there's something connected on the inputs. When there's nothing there, the output sound/playback is perfect

Erik, I hear it through my headphones, I have no speakers...I do hear the hum when the cables alone are connected, although they're much louder when I plug instruments/mics

Thanks, Erik, I'll try the isolator then...I can't really disconnect the USB because the Scarlett 2i4 has no external power source, it's powered solely through USB, so I need it connected in order to hear anything. The hum goes away when I disconnect my notebook power cord, using the battery...But anyhow, I had not heard about these USB galvanic isolators, I'll give them a try.