I've got the 100w EL34 head and had the same issue. What kind of lighting is in the room/rooms you're playing? I found just the red channel on mine picked up noise from LOTS of stuff including the fluorescent lights in my home. It literally sounded like it was amplifying the gas cooking in the light tubes/jet engine during take-off. I also found some noise in the cables I was using. I switched cables to Mogami Gold, the only place I can do anything about the lights is my house, so I changed all the fluorescents to LED bulbs. I put a MXR Smart Gate in the effects loop and it helped a little too. The noise level is much better now.
FWIW, I went as far as taking mine to Guitar Center and compared it to the 5150III 50W EL34 head and a 15W EVH Lunch Box. All of them had the same amount of noise on the high gain channel. The whole line is notoriously noisy.