[Bogdanoff]

This was transformer hum. The unit hummed whether it was connected to another device or not. Pulled the power cord, it stopped humming. No signal hum. I could detect hum through the open headphones during quiet passages, turn the volume up and mask the hum.

I had the same problem with mine - turns out it's insufficient shielding as I had my amp stacked on top of yggy - creating a larger air gap got rid of the humming. I still can hear some hum from the unit's transformers without any headphones on as I sit very close to it but it's not audible through my headphones anymore.

 

[Kristofa]

My Loki Max had excessive hum when stacked so I now keep all my Kara, Loki Max, and GS2 on their own shelves.