Try testing with audio set to Direct Sound or WASAPI.
Describe your setup in some detail.
Audio route is OK, I don't hear any noise. Audio is going via ASIO into dedicated USB DAC, then dedicated stereo analog preamp.
Video is configured as separate zone, bitstreaming via HDMI to multichannel preamp, from there path is the same to speakers
What changed this month is that
- new PC. Faster and using switching, but passive power supply. Both were using Streacom FC5 chassis, all passive components
- new MC 27 (with license for 28)
What is interesting is why do I hear this noise only when playing back video, and during pause?
Could it be MC27 is sending also something on HDMI along the original signal? I don't know, just guessing..
I would say it is a ground loop? but why do I don't hear it when MC is not playing, and not during audio playback?
During audio playback, the same video path is used - HDMI from the same audio-pc to the multichannel processor and from there to the monitor