Like erik squires said in his post, it could be DC on the AC mains. If that is the case it’s not the fault of the power transformer of the amp.
Things that can cause DC on the AC mains, light dimmers, switching power supplies, micro processors that use switching power supplies, hair dryers. Could be any of these things caused by a next door neighbor that is fed from the same utility power transformer.
Take the amp to someone else house outside of your neighborhood and check the amp for the mechanical vibrating/hum.
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Things that can cause DC on the AC mains, light dimmers, switching power supplies, micro processors that use switching power supplies, hair dryers. Could be any of these things caused by a next door neighbor that is fed from the same utility power transformer.
Take the amp to someone else house outside of your neighborhood and check the amp for the mechanical vibrating/hum.
.