Question Interference from PC - also affecting external amps

Oct 23, 2019
ASUS Sabertooth X79
Intel i7-3960X 3.30 GHz (factory clock)
Geforce GTX970

Performance diagnostics: Report here

For the longest time I've been struggling with snapping, crackling and popping when using an external sound card (Steinberg UR22) to send audio to my Yamaha studio monitors. This problem did not arise until I moved apartments three years ago. The exact same rig with the exact same setup was causing interference. For the longest time I suspected a ground loop, but the other day I remodeled my apartment, and moved my PC into my living room. About 2 meters away from the case itself is my guitar tube amp. This lead to me discovering that the magnetic pickups on my guitar also pick up the interference.
Edit: Forgot to add that I do not experience any interference when using a headset directly into the integrated audio.

I have googled this problem to death. Some things I have already tried;
Disabling on board audio
Plugging speakers/pc into the same power strip
Plugging them into different power strips
Installed a surge protector and power "purifier"
Using the external sound card and studio monitors on my laptop (no hissing there)
Unplugging all peripherals
Reformating the drive

The turning point for me is that my guitar is also picking up the noise. This leads to me thinking that there's something inside the PC itself causing this interference. Could a component have been banged up a bit since the move 3 years ago? Since then I've only exchanged the cooling system and GFX card, but the problem arose before switching out the components. Could it be PSU related? I don't have a lot of spares lying about to figure this out, and I'm a broke student. Any ideas as to what I could try to mitigate the issue?