I had similar problem and similar setup few years ago. Got some interesting sound anomalies occasionally, opened a folder, opened program, moved files around... I have "short fuse", so I started to troubleshoot what the heck caused that noise. It took few minutes to find out it was my external HDD at that time, USB powered one to be specific.
When my PC accessed that, it caused interference that I could hear through my speakers. No matter what USB port I picked it made the noise, so I had to change the outlet. I took my PC off the power grid that my amplifier was plugged in and just straight up plugged it to free outlet I had nearby. Never heard that noise again.
Fast forward to this day, I have active studio monitors. These damn things will make noise If I put my phone right next to one, I can hear faint "bzz bzz bzzzzzz bz bz bz.." all the time. It's not like the one you've heard from car radio, caused by mobile phone interference.
So, I recommend you to unplug peripherals that you think are causing the noise, if possible, start moving your stuff from outlet to outlet and separate things like PC and amplifier, monitor and amplifier and so on. How is your analog input by the way? How is it routed?