We have a humming sound coming from behind the upper freezer area. It is not the ice maker. Comes on when we open and shut the doors of either fridge side or freezer. Sounds like a fan that is laboring, and will speed up, then sounds like it is slowing down. Sounds like a blade that needs oiling??? :rolleyes:
The freezer is still freezing foods and fridge size is fine as well, but do not want to wake up to any melting surprises or food loss. Can you help explain what this might be? 
Serial number is AA213239
THANK YOU!