I had all the same issues with my Freya N that you guys are describing. Two different units. I tried every combination of XLR and RCA input/output. I tried the new tubes that Schiit sent me. I tried multiple sources, and multiple power amps, but the popping and volume jumps persisted.
To me, it seemed to be some kind of thermal issue. When I first powered on the Freya, and used it in either passive or jfet mode, I had no issues and everything worked perfectly. It was only after being in tube mode for a while, and the unit got hotter, that the popping would start. Once the Freya was hot, I could switch it back to passive or jfet, and the popping would persist in those modes as well until it cooled down a bit.
If I had bought this Freya used I would have been slightly perturbed, but would have learned to live with it because it sounded great. Lord knows I've had enough vintage gear with quirks. But this Freya was brand new, and shouldn't have ANY quirks, so I decided to return it. I ended up getting a Freya S and the volume control works perfectly, so I'm happy. I hope you guys get yours figured out.