Sometimes, ice can block passages and cause problems.

After doing a lot of research yesterday I have reached the conclusion
it's may be a defective defrost timer.

I suffered something similar: an old frost-free fridge
was making noise from the fan hitting ice that built up on the coils.
The defrost timer was behind the fridge in the bottom left:
a mechanical motor like a wall clock,
with a little window to see the rotor spinning.
Giving it a shake-n-twist got it spinning again.

Happily it was stuck in the "run" position,
not the "off" position or with the heater on to melt the ice.

Perhaps you can solve the problem the same way?