mhdt Orchid - hum noise

Hi all

I have been having issues with my Orchid (again) but this time is more frustrating. I hear a very strong hum noise when the dac is turned on and it doesn't go away, even when playing music, even if the music masks it a little. The noise is very evident and I'm wondering if not working properly and I'm afraid the dac will stop working all together any time. I have changed power cables, connection cables, tried 3 different tubes and the issue is there with zero improvement. The hum gets louder as I turn up the volume.

Did any of you ever experience this issue? 

any suggestion on how to solve it is welcome.

thank you in advance.

Nuno