Noise in the phones out.

Hi all,
For the past year I have this “thing” with my headphone outputs. There is a pretty noticeable noise-hum kinda sound coming out of both the head outs. The strange thing is that as I increase the volume (not the mains just for each headphone’s out separately) the noise starts to fade out until 3 to 4 o’clock which is barely noticeable (thank god!) and from that point on until 0db in starts fading back in.
(To catch up I must tell you that I use a ups for the MR(-816x) and the pc)

The overall “audio” quality of this thing is astonishing but the software implementation (until now at least) is poor to put it
I mean I finally got it working but man…

Anyways I would love to hear some feedback-comments-suggestions from other experienced users here.

Have a nice summer.