I have the exact same problem with Sony pha3 with active speakers but absolutely no noise with headphones
I assume that it's because sony pha3 is originally made for headphone amp
desktop powered + usb -> noise
adapter powered + usb -> noise
desktop powered + toslink -> noise
adapter powered + toslink -> no noise
notebook plugged -> noise
notebook on battery -> no noise
would balanced connection solve the problem? because both pha3 and my active speakers support balanced input output
I could imagine my noise is what they call RFI and I think the noise very related to mouse, keyboard interactions and graphics card