Humming Noise in Electrical Cable Area

do a search for ATS (automatic Transfer switch) humming, lot of info on the forum about this. possibly your issue.

If you have a generator then I'm sure its the transfer switch (gen/shore switch) making a humming noise. Pretty common for some transfer switch models. Sometimes you can take the contact points apart and clean them up to see if that helps (power off obviously) or look for a better model less likely to hum.

I had a Dutch Star for a few years, I had similar, It was the Power Converter/charger - that rig has a seperate Inverter/Batt Charger. The Charger was in a compartment under the bedroom slide. The fan was going and making a noise - I replaced the charger.

Fan on converter trying to cool it down, Fan is a 12 volt device.

Crickets

Battery disconnect Switch? Neighbors Jayco has a relay disconnect switch.Needs power to hold it closed. Quite (no power) when off.Should have been a latching relay so power is only needed to make the switch. Don"t know if that is what you are hearing though

Possible the Converter Fan is running which will run even after 120 disconnected until the converter cools down. If you have an Inverter/Charger, you will not have a Converter. The standard Converter is in the shore cord Compartment on a Newmar. The optional Inverter is on the Passenger side. On your Newmar in that compartment you have
The Transfer box
The Converter/s if you have them, your model may have 2 converters
The Power Cord reel
The BIRD control relay(this will not make any noise)
The Emergency Start solenoid
The Battery disconnect Solenoid Doug