My desktop PC and monitor and active speakers are all connected to one socket via a power strip. Over usb, signal is sent to my schiit fulla 2 DAC/preamp (which in addition to receiving power over usb, receives power from a separate wall plug) which is connected to my JBL LSR 305s via a 3.5mm to mono left and right 1/4" trs y split cable much like this https://www.gear4music.com/G4M/Klotz-Y-Cable-35mm-Twin-1-4-Cable-1m/2557 (but by yamaha).
In this config I get a horrendously loud static/white noise sound with intermittent high frequencies (think screeching sound).
What I've tried:
Connecting the fulla usb to a laptop instead of the desktop - this results in basically no audible white noise at all, regardless of whether the laptop is charging or not.
Connecting the 3.5mm end of the cable directly to my mobo - this is in effect worse in every way. The static shifts to be even more high pitched and I can now hear high pitched frequencies much more, especially when scrolling or moving the mouse.
Removing the separate power source for the fulla 2 - results in more high pitched screeching. I've heard this is due to noisy vbus on usb.
Building and using an entirely different desktop pc - same as before.
Switching plug sockets, even from a completely different room - no difference in results.
Removing all usb and ethernet cables connected to the pc - no difference.
Turning off and removing the DVI monitor - no difference.
I've checked the motherboard standoffs and they seem tight with good connection. Power supply screws that ground the case seem good too. My worry is that they are painted screws which may interfere with proper grounding of the case and hardware, and that I've read that the middle most standoff for a motherboard should be plastic and is metal for my case (Phanteks Evolv ATX).
This has been going on for a while and recently got even worse despite no changes made by me. My PC sits under my Ikea chipboard desk, the speakers sit above (on a few books) and I try to route all power cables separately to the usb and audio cables.
Increasing the volume knob on the speaker increases the volume of the white noise/hiss/static and screeching but changing windows or preamp volume changes nothing.
mobo: MSI B350 TOMAHAWK AMD B350
cpu: Ryzen 5 1600
gpu: Gtx 660 gigabyte windforce OC
psu: EVGA supernova 650
OS: windows 10
ram: corsair LPX 3200MHz
500gb Samsung ssd
mouse: razer deathadder
DAC/preamp/headphone amp: schiit fulla 2
Active speakers: JBL LSR305
Please let me know if there's a better place to post this question, maybe even an entirely different website! Please do offer any and all help. I am on a limited budget here, so I'm afraid I may not be able to buy isolators / usb hubs just to test.
I just want this noise to be gone/ reduced to the level that I can enjoy using something that is admittedly a sizeable purchase for me.
Thanks very much for your time,