a cheapo ground loop isolator. It did the job. BUT, it destroyed lower frequencies.
Yes, making a transformer which can pass low frequencies and has good high frequency response is somewhat tricky.
but the sub has only RCA and balanced TRS inputs as passthrough.
So the sub has the crossover, and the L and R combined audio signals go to the sub, and from the sub then go to the small monitors?
That makes it a little trickier, the transformers optimized for low frequency performance do not have extended high frequency performance.
A standard Jensen isolator would probably work fine, if the system has RCA inputs then the levels are not very high so there should not be a huge problem with LF distortion.
I'm hoping that the motherboard replacement(Which is still in warranty) fixes the issue for me since it only happens when connected to the PC. If that doesn't work, I'll try a PSU replacement (Also within warranty)... If that doesn't work, I don't know what to do.
It doesn't seem likely, you have not described anything else about the system to indicate that it is operating differently than designed or expected.
But its weird I only have issue when I connect the whole set up to the PC specifically. Laptop, Switch and PS4 work just fine.
The PC is probably on the order of 10x higher power than the laptop and PS4, and more like 100x higher power than a Nintendo Switch. Interference is often dependent on the currents involved.
You can get some relatively inexpensive USB isolators, I see some in the range of $10 to $20 on Amazon. The cheapest one doesn't have a case, you could try that and if it works well enough you could 3D print a case for it, or just wrap it up in mylar tape or whatever. Or just pay the extra $10 for one that comes in a case.
PS4 I use the optical out which if I'm not mistaken carries no current, right?
Right, optical connections are electrically isolated. Electrical isolation is what you need, to keep common mode currents from the high power PC power supply from flowing on the audio lines. Optical connections work, transformer isolated S/PDIF
would should work, or isolate on the USB side.
Granted the Switch and and Laptop are all DC powered devices
Probably more relevant is that the laptop is low enough power that it would have a much milder AC filtering at the power brick inlet, so much less leakage current. At least I assume you tried the laptop with it connected to the charger, if it was unplugged and only running from battery then that would obviously be a completely different situation than the PC, but if the laptop is plugged in to the charger then it is just a lower power version of the PC.
