My two cents. In the vicinity of the breaker panel you are close to the Inverter/Chargers. If one of them is working hard you could hear a hum inside the Bus. After sitting without power they would want to charge the house batteries. Is it possible even though the remote switch plates say the chargers are off one is actually on and trying to charge because the remote switch is in the wrong position at the Inverters ?
Barney, you're doing a good job on this issue. Tell your wife it will not always be this stressful. It just takes a while to work your way through the " New Ownership Issues ."