The vent door in my refrigerator made a very annoying clicking sound as it opened. The problem is the motor/gear assembly in the control unit.
I replaced it with a new a new and the problem went away. Replacement was easy - remove the vent door, remove two screws, unplug the control wires, and pull the old unit out. Reverse these steps to install the new unit.
Note that this is the second control unit to go bad. I ordered two replacement units because I anticipate the control unit will fail again in about a year.