OP is it that most tube amps have too low a signal to noise ratio? Or some other factor?
The reason why audio systems are noisy because all audio systems sound unnatural. The natural sound is very quiet.
In below video,
1) From 0 ~ 0.07, both spkrs sound fine because your ears adapt quickly to sounds.
2) 0:08 ~ 0:22 the natural sound spkr sounds quiet (no bad noise) and fine.
3) 0:25 ~ 0:35 the unnatural sound spkr sound OK (with some bright noises), your ears quickly adjust to the unnatural sound. ** Your ears are biased and in unnatural sound mode now.
4) 0:37 ~ 0:44 the natural sound is weak and unclear because your biased ears are not quickly adjust to the natural sound since unnatural sound is powerful and harsh. Natural sound is soft and delicate.
5) 0:52 ~ 0:59 Your ears recovered with my voice support. Your ears are in natural sound mode now.
6) 1:00 ~ 1:25 the natural sound spkr sounds fine.
7) 1:27 ~ 2:00 Your ears are confused between natural sound (my voice) and unnatural spkr sound. Your ears switch very fast between my voice and spkr sounds to comprehend both. **Lot's of listener's fatigue this stage. All hi-fi systems sound/behave like this and results much listener’s fatigue between natural sounds (dog’s bark, kitchen sounds, people talking, car sounds, etc.) and unnatural audio sounds. Therefore, hi-fi audio listening is preferred at quiet late night.
8) 2:05 ~ 2:18 your ears are easily adjust to the natural sound with my voice. Notice the natural sound is very quiet.
All audio systems in the world behave like the left speaker and you will hear some noises from an audio system. Alex/Wavetouch
Killing me softly - (Natural vs. Un-natural sound), PA speaker comparison.