This is getting ridiculous. I've submitted 3 tickets to Massdrop regarding an issue that I'm having with the amp. It's been more than a month since my first attempt to contact them. For the first couple of weeks of being with the amp were great but now you can hear faint crackling noises in the left earphone you can also hear taps on the amp and switch in the headphones as loud thumps. Please contact me back so that we can work the problem out.
The stock tubes are terrible. What you have sounds like you got noisy tubes. I had that couple times with two different tube amps I have. Try replacing the tubes.