If I may ask, how did you solve the problem?

If I may ask, how did you solve the problem?

I've had problems like that too and it always had something to do with a ground loop.
- Auzentech Forte 7.1 needed an isolated PCI slot cover in order to be silent
- Auzentech X-Fi HTHD needed the same isolated PCI slot cover but still had some noise depending on opamp choice
- Little Dot MK V needed an isolated grounding cable (inside the box) to remain silent
I've always used my pair of 32 ohm Ultrasones with them so I guess some higher impedance phones would have been silent right away as I don't have any other grounding issues anywhere else around my house.
I'm still waiting for a'444 to return from the shop with a follow-up reply. And see what that reads like...
A similar problem fix is change the mouse to a front port.