If you were full of magnetism you might buzz too. But seriously, it's a transformer buzz. As they age, the irons might get a bit loose, and they buzz when they used to just hum.
Experiment a bit, take the breaker cover off and have a listen when you are down low, then turn on as many silent loads as you have.. lights. See if it buzzes more. If you have LED lights you are only producing a couple amps, but if you have incandescent you have an amp per light bulb.
Nothing to worry about though. If you are really curious, get a laser thermometer and record the lights and the temperature, then see if it changes in a year or two.
While you are doing this, tighten all the screws on the 12 volt positive and negative terminals, especially the big wires that go from the converter to the battery. That can be a source of problems too.
Mike
2012 Winnebago Impulse Silver 26QP
2005 16.6 Double Eagle
2018 Jeep Wrangler JK
previously Snowbird Campers,
Triple E Motorhome and Fifth Wheel