Potential Ground Loop Problem (Help!)

Hi all,

I have a problem, so I thought I'd ask here since I got some very helpful feedback last time I had a problem.
There is a constant buzzing sound on my amp's (SMSL 98E) outputs (which scales with the volume dial) whenever I plug in a device with an AC connection. This does not happen when I plug in my phone, unless the phone is charging, in which case the buzzing persists. I have the amp hooked up to my focusrite solo, which in turn is plugged into my PC's motherboard USB ports. 
Things I have tried:
 - Using both an aux to RCA cable, and two 1/4 to RCA cables to connect the focusrite to the amp
 - Unplugging all usb and display cables from my PC except the focusrite
 - Unplugging all cables from my monitor except AC, and connecting the monitor to the amp with the aux to rca cable.
 - Plugging all components into the same extension chord / outlet. 

Interesting fact: When I move my mouse or use my keyboard, which are both plugged in through usb, I can hear the buzzing get worse for the duration that I use my peripherals.

From reading online I thought it could be a ground loop problem, which could be solved by using a ground-loop isolator, but I'm not sure and I don't want to start buying things without knowing what I'm dealing with.

Does anyone know what the problem could be?

Any help is appreciated.