Don't mean to disappoint you but the valvetronix amps are not exactly tube amps but rather a hybrid, in essence, a solid state amp that has a 12ax7 somewhere in the circuit.
Here is an explanation "the Valvetronix amps use a 12AX7 tube (commonly used as a preamp tube in a tube amp) run at the correct specified plate and heater voltages, then coupled it with an actual output transformer prior to sending the final signal to a solid-state amplifier".
I guess that doesn't answer why you're amp is making all that noise. I suggest bringing it to an amp tech. I honestly don't think replacing that single 12ax7 is going to make the noise go away.