I am having the same problem. I have taken out the freezer drawers and removed the internal back cover. Behind this is the fan. The blades on mine were catching on the the plastic housing which is wearing away. I have pulled the fan forward so it misses the plastic which has allowed it to run quiet. However, this is not a permanent solution. Maybe I need to fit a new fan. Re-assemble. Maybe if I also tilt the fridge very slightly forward the fan will remain clear of the plastic housing and therefore not catch. Note, I know nothing about fridges, I am a general DIY'er
Pete Stafford, July 2010