No expert here.
First, try switching the tubes. If this does not work, try replacing them.
Then, if the hum remains, call the manufacturer.
Audible Hum From Integrated Amp
I am getting a low volume but audible hum from my Rogue Sphinx. I also hear volume changes through the speakers ( with no music source of course). I have tried other amplifiers in the system, no hum. Any suggestions on what I might do to eliminate this fairly minor but annoying problem? Thanks .