Frig Door ajar alarm
Had the identical issue on our maiden voyage. First, make sure the door is completely closed. It is indeed an alarm that's telling you the door sensor doesn't think is closed.
If that doesn't work, try unplugging the fridge light. The sensor may be defective, and by unplugging the fridge light you fool the sensor into thinking the door is closed. It will silence the door alarm, but you'll need to get the light assembly/sensor replaced - that is, if you want a fridge light.
"You can't buy happiness, but you can buy an RV. And that is pretty close."