Tube noise when gain is increased, tube issue?

microphonic tube. Switch tubes and see what happens.

If it is only one tube try another.

It's a schit Freya preamp with 6sn7 gtb tubes. 

Finding low noise 6sl7's can be difficult and expensive but that may be the only solution to your problem. What is the sensitivity level of your speakers? If it is too high then perhaps its not so much the tubes as the interface between your amp and speakers.

BTW, what brand of 6sl7's are in your Schiit now?

Most tubes have some noise, some less than others...unless it's humming or buzzing, and does not interfere with the music being played, I'd not worry too much about it.

I have about thirty tubes in my system… no noise… no hiss, no hum or buzzing what so ever.