I pulled this info from the internet. This appears to be condensation in the door latch alarm. Some people use a can of compressed air (for computer keyboards) to dry the wires/circuit board.
"The problem lies with the wires and plug into the rear of the lamp unit becoming coated with condensation, which somehow activates the warning system - 30 beeps for 20 seconds repeating every 2min 40sec.
The cure is to pull off the plastic cover over the lamp unit, dry the wires and plug, and all is well - until the next time I assume.
A feature of the "fault" is that the fridge does keep working despite the alarm, so there's no need to switch it off if you can put up with the beeps until you are advised of the cure - OK if you can go out for a walk, but no good to sleep with."
Rush 19 Toyhauler