Electrical buzz

Sounds then like one of the relays has a loose coil. Some are replaceable.
Make and model of transfer switch?

Yes. Removed drawer to access transfer switch. Definetly coming from transfer switch housing.

Have you tried to locate source by sound?

Not driving. Plugged in to 50 amp service on Oregon coast. Has been buzzing for 3 days.

Buzz does not sound like arcing. 2 very distinct sounds.
Since this happens while you driving, are you running the generator? If yes possible it could be the ATS relays chattering. If not then you need to isolate when it happens, what is turned on AC, generator or shore power. No AC only DC on. What is in that area.

Otherwise everyone is guessing.

Inverter? My fan comes on when the load on the 12v system gets higher, it charges more, fan speeds up.

No, the breakers only trip on overloads and heat. Surge protectors stop excessive voltage.
I would try to listen and isolate where the sound is coming.
Could be a loose wire nut in the junction box by shore power entrance.
Could be behind the metal dead front covering the 120 volt circuit breakers. Disconnect from shore power, remove dead front and check all connections. It would be wise to get some electrical grease before starting this. Disconnect each wire, one at a time, inspect for heat damaged insulation or burnt wire. Then coat wire with electrical grease and reconnect.

Yes,2011 fleetwood southwind 32vs. If there was something causing an arc,wouldn't, the breakers,fuses or surge protector shut down?

It could be a loose connection arcing. Could be very bad!
Is it a thirty or fifty amp?
Is this in the 2011 Fleetwood 32VS?

First thing to do is post the year, make, model etc of your coach..too many things it could be....without that info will get you no help, sorry.....Dennis