hi..sorry for delay..i cleaned out the fan..it only had dust in it no real obstructions..i can feel the vibration in the middle of the refridgerator about 3 feet from the ground..
It will be the evap fan. If it is realy bad you may just need the fan blade if it is missing a fin. Other wise replace the fan. Unplug the unit and remove the rear panel of the freezer. There will be 3 tabs on the vent cover to remove it. Look for the picture of the screw driver on the cover for the two outside ones and you can see the one in the center. You will also have to release the keeper clips on the side of the ice maker plug to release it from the back panel.
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You will need #318 if the photo. You can use the OEM part number at your local parts store also.