Welcome to the forum.
Aren't hornets supposed to buzz?
I had an issue like this with the S&B panel; faulty breaker. Replaced and the noise went away.
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Now: 2019 Winnebago 2500FL w/e2 WDH;Sold: 2015 Bullet Premier 19FBPR (shown)
2012 Ford F-250 Lariat Super Duty Crew Cab (gas 6.2 L, 3.73 gear ratio 2WD, 172" WB)