Left fan on my macbook pro has was going out. Made the absolute worst noise I have ever heard a laptop make. Was also causing my computer to run hotter than normal due to the fan not spinning properly. I finally decided to fix it after the noise went from a slight rumble to a death scream.
The repair was very easy. Took me all of ten minutes to replace.
The only thing I can think of in the way of advice is just be sure that when removing the connecter for the fan be sure to pull it straight up.
Also after removing the back cover and seeing all the dust collected in the fans and dust traps I would recommend hitting it with some air duster maybe once a year or something like that.
Phillips #00 Screwdriver
TR6 Torx Security Screwdriver
MacBook Pro 15" Late 2008 through Mid 2012 (excluding Mid 2009 2.53 GHz) Left Fan