I hope I'm in the right place. I got hearing aids back at the beginning of the year and finally got them adjusted to eliminate phasing that made my guitars sound like they were being played through a chorus pedal. So now I can play with the aids in. Tone, timbre, and balance between strings are all improved. That's great but I hear something unpleasant with my hearing aids in. My amp is a Mesa Boogie Express 5:25. The problem I'm noticing is hiss from the power stage. I never noticed it before I began using my hearing aids. The hiss is loud enough to bother me at bedroom volume. It gets louder when I turn the volume up and decreases when I turn the volume down. The hiss is independent of the volume setting on my Stratocaster. The hiss is not 60 cycle hum. I can hear that if I listen for it, but my FCS Strat is shielded well enough that it isn't bothersome. I use only one pedal, a BOSS EQ-200 and the hiss is independent of the pedal or pedal settings. I can reduce the hiss by reducing the volume on the amp and raising the gain but that puts the volume at about 9 o'clock and I loose harmonic richness with the volume that low. I replaced the power tubes with new tubes from Mesa Boogie about 6 months ago. The last ones lasted years, not months so I don't think the power tubes are shot. Is there something I can check? How much hiss is normal? Can low noise power tubes be had anywhere? Mesa Boogie makes a big deal about selecting tubes that don't need biasing. What are the risks of using matched tubes that may need a different bias from the preset? I love the amp. I want to keep it. I don't want to go solid state. Am I just overly sensitive to this? Somebody tell me there's a way out of the maze. Thanks in advance.