Single coil pickups, by their design, convert electro-magnetic energy into electrical energy. Those little, subtle, wobbles of your strings, wibbling about in the field of your tiny little magnets. When we had real tubes in our computer monitors, it was pretty bad, and of course, close. It got better when we swapped to flat screens, but got worse when switch mode power supplies became everywhere. I have found these the worst generators of noise, some crazily so. Often the noise they generate propogates through your house/studio mains power wiring, spreading out the origin point over a wider area.
It is well worth it to pull everything you can, that is not essential. So strip down what you have to a minimum. Unplug everything bar the computer, monitor, interface. Dont even use amps and speakers, but headphones. Absolute minimum gear, and see how noisy that is. Add your kit, one by one and see if you can identify one specific item. For me, in my video studio, it was the 4 port network hub. One other thing caused grief. My Adam speakers. Plugging in these caused some kind of grounding issue, and these now have their audio going through a transformer isolator. In my home studio, these monitors are silent. I neverr found the cause, but the isolator cured the noise, presumably coming from something else.
Plugging in a Les Paul produces just guitar. My Strat just hates my studio. At the theatre I look after, I sometimes see single coil players struggling with feedback and weird whistles and noise. I quietly walk up to the rack, stage left, and turn off the hearing loop, and the guitar behaves. Not every guitar with single coil pickups, not the same make, or pickup brand. Has the guitar got shielded pickup cavities, or screened cable between pickup and switchery? No idea. Just happens.
