I had a similar problem with my Samsung side by side refrigerator, the fan was making a noise - sort of grinding and would stop every time i opened the fridge door and then continue when the door was cloased. Pretty soon the noise stopped and so did the cooling inside the fridge. I thought the fan might have stopped working so i followed the steps in the post above to remove the bottom panel, which also requires removing the top light housing cover.
When i got the bottom cover off, an this is mounted the fan by four screws, remove these and the fan assembly comes off - becarefull of the wires!, i noticed that there was a large lump of ice that was blocking the fan blades towards the bottom where there is also a hole i think for allowing the cool air to come in. So to clear the ice i placed a large amount of salt and warm water, left this to take action, once all the ice had melted i flushed this through with warm clean water, wiped down and reassembled the items in reverse oder.
Thats it, now the whole thing is working fine.
Hope this helps someone else with similar problems.
Kash, July 2007