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.
santiagol
Post removed 
PC's are notorious for causing ground loop issues. You can test this out with a laptop which can be unplugged from the wall, or by turning off the PC and disconnecting it.

If you are using a USB connector, use a USB isolator.

Best,

E
@erik_squires 
@cleeds 

I found the source of the issue: my PC.
I tried using my laptop and my phone as input sources and in both cases the buzzing was gone, even when I plugged them in to the AC. 
I'm going to blame my motherboard for it, since I already have 4 usb ports that don't work properly. A psu issue isn't out of the question for me.
I think I'm to buy a USB isolator. I'm unsure whether a pcie hub would fix it, although if it did I would be happy since I've been looking to buy buy for a while now anyways.

Thank you for the help,

Santiago
I wouldn't blame your PC so much as it's power supply.  A USB ground loop isolator is the right solution, though they don't always work with every DAC.