Loud noises prompted me to take my Macbook Pro to the Genius Bar. They wanted to keep it for 3+ days to replace the fan, at a pretty significant cost. I happen to be blessed with a very smart teenager who cut his teeth on taking Mac's apart. Quick order on iFixit, an even faster delivery, and voila!
Simple simple simple. Took my son about 15 minutes start to finish. Great tutorial. I'm a first time ifixit customer, and you've got me for life. Thanks!
Follow the tutorial exactly, and if you're at all hesitant, seek out a smart neighborhood teenager to do the job for you.