Side by Side fridge/freezer still cools, but tops of both compartments is warm, and bottom of each side is below freezing. Condition started about 1 week ago. I notice that the air that blows inside in fridge during a cooling cycle is not blowing.

Before this started, had been having a knocking sound for 20-30 seconds after most cooling cycles for at least the past year. Then about a week before the unit stopped blowing the chilled air, had been hearing an "electronic" buzz that lasted 5-10 seconds that sounded like some electronic process trying to start.

Fan outside the unit still working.

Do I just need to replace the other fan, or are there other potential complicating factors that I need to be aware of before replacing the fan that circulates the internal chilled air?