Tube noise when gain is increased, tube issue?

Sounds like noisy tubes. Could be a noise floor issue depending on amp/speaker/ interface especially speakers with high sensitivity. I like the former if for no other reason than it is easier to solve.  

What brand?  What tubes does the manual call for?  What tubes are in there?

Buzzing or humming is usually from the transformer and can excite a noisy tube. If you don't need the extra gain, switch back to low gain, it is always quieter.

Russ69, FWIW I think OP was referring to using his attenuator to adjust gain. At least that is how I read it.

Russ69, FWIW I think OP was referring to using his attenuator to adjust gain. At least that is how I read it.

Oh, OK. I guess he is hearing tube noise when he turns up the volume and nothing is playing? Lots of questions in that case. Is this something new? Do you hear the noise when playing music? What preamp?

I always have an extra set of tubes around. If there is a strange behavior… I swap out the tubes to see if it ends. It usually does… then I swap the old tubes back in one by one, until the problem comes back. 

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.

I have the Freya, no hum or noise at any level. Guessing you have a bad tube. 

The Freya is known for this problem. Do some research and you will find that you are not alone. You might be able to find a better tube but you also might be chasing your tail. I have had 6SN7s prove noisy in Schiit products that are not noisy in all other applications and for this reason I will not retube any Schiit product. I have even hard clients that had Schiit "selected" tubes go noisy in a very short period of time. I had heard that they improved this component in this regard with later production units.

BTW humming and buzzing are not typical indications of a microphonic tube. Ringing and howling are more typical.

I know this is a late response; but...

I’ve had the same problem with my Freya+; chased it around awhile and in the end replaced ONE tube. End of problem for the last 2 years...