Are we talking about hiss or (mechanical) hum?
I have more than 1 system where I can power everything up, crank up all of my gains and volume knobs with no material playing, put my ear right on the tweeter, and hear absolute silence.
I cannot always achieve that goal, but that is my goal. If I can't achieve that, then you can start tweaking down the gain knob until you get dead silence. At that point, any hiss won't be audible once the music is playing anyway.