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Try replacing the phono stage tubes with some tested as low noise/either gold or platinum, as described on the following page. Of course Kevin isn’t the only tube seller that grades for low noise. (https://www.upscaleaudio.com/pages/grading-matching) Then too, it could be that your cartridge’s output is too low for your phono stage’s gain capabilities, and requires you to crank the volume. That can enable one to hear even the quietest phono stage. Before anyone suggests tapping on your tubes(yes- I have), there is some good info, toward the bottom of this page, regarding microphony: (https://www.upscaleaudio.com/pages/tube-basics-and-frequently-asked-questions) It could also be as simple as dirty tube pins and/or sockets.
That sound upon powering up is highly consistent with "tube rush". In some instances but not yours the sound disappears.
It is a good time to get new tubes, per Rodman 99...You should try to get very quiet selected tubes. A phono stage in particular requires the least noisy tubes you can get, (most of them anyway)