What causes ice buildup in back of freezer?

What is the model number of your unit?

What is the model number?
The ice maker will only run if the freezer is at the correct temperature.
Do you see any ice buildup on the back wall of the freezer or behind it?

Do you see any ice buildup on the back wall of the freezer or behind it?

You hear the evaporator fan that is probably rubbing on some ice buildup. Remove the rear panel in the freezer to confirm that there is ice buildup and post back to me.

Do you see any ice buildup on the back wall of the freezer or behind it?

If noise stops when you open the door, you may have a noisy fan (or could have ice build up, causing fan blade to hit ice and cause noise). I gather it is a frost-free model ie has a fan in the freezer compartment. If noise is caused by fan hitting ice build up, you may have a problem with the auto defrost system, as you should not get ice build up in a frost free.
Noise stops when you open door because fan turns off when door is opened.

Sounds like a defrost problem. Check to see if there is any frost buildup in the back wall of the freezer. If so, it is not defrosting as it should.

• possible causes:

1. bad defrost timer/control board
2. bad defrost heater (in freezer)
3. bad thermo switch in freezer

If you don’t know what these are then unplug the machine and let the ice melt in the freezer overnight with the door open. Then try it the next day, if is cooling fine then you need to have a service person replace one of the above items.

Sounds like a defrost problem. Check to see if there is any frost buildup in the back wall of the freezer. If so, it is not defrosting as it should.

• possible causes:

1. bad defrost timer
2. bad defrost heater (in freezer)
3. bad thermo switch in freezer

If you don’t know what these are then unplug the machine and let the ice melt in the freezer overnight with the door open. Then try it the next day, if is cooling fine then you need to have a service person replace one of the above items.

Sounds like a defrost problem. Check to see if there is any frost buildup in the back wall of the freezer. If so, it is not defrosting as it should.

• possible causes:

1. bad defrost timer
2. bad defrost heater (in freezer)
3. bad thermo switch in freezer

If you don’t know what these are then unplug the machine and let the ice melt in the freezer overnight with the door open. Then try it the next day, if is cooling fine then you need to have a service person replace one of the above items. If it still has a problem then it might be the compressor and you should probably replace the machine.

Sounds like ice buildup around the fan that's inside the freezer.  My lousy GE 3-door did that when the bottom freezer didn't get completely closed overnight, and everything behind the back panel, where the coils are froze up like an iceberg.  I had to take the back panel off and melt it with a hair dryer. 

See if you see any abnormal ice buildup, or if the refrig compartment is getting warm.  That's usually a result of ice buildup.   Another cause is a failure in the defrost cycle.  It will freeze up after a couple days. This would usually be the defrost timer.