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All tube amps have inherent thermal noise. It is perfectly normal...signal/noise ratio is seldom better than 80dB, depending on design.
Troubleshoot this way:
Disconnect everything but speakers from the amp, short the input connectors. Noise still there? If it is white noise (and not 60Hz hum), and roughly same level on both channels then I would say there is nothing wrong except that tubes are maybe getting old. Record the noise and upload it here otherwise.
First stage tubes are always microphonic...it is the nature, they are amplifying very weak signal, thus very sensitive for vibration.
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Thank you for your time,
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