Our refrigerator (residential) in our Tuscany 36mq clicks about every 20 seconds or so. The noise is coming from the rear. I can also here it on the outside of the RV if I stand close to the panel that opens to the the reefer power plug. The ice maker is turned off. The reefer temp is at a nominal level, but not as cold as when we use it. There is about 10 gallons of fresh water in the tank. The pump is not running and the line has full pressure.
Our frig at home will do that when a piece of ice gets stuck in one of the the ice maker slots at the top of the assembly. Even if your ice maker is "disengaged" it will still try to clear the piece of ice.
That would be the only thing I can think of.
Full Time in 2017 Newmar Ventana 4369
pulling a 24' enclosed (Mini Cooper/Harley/Kayak)
(traded 2014 Thor Challenger)
US Army 70-73 Retired LEO