A year ago, the right fan started making noises. At the very beginning, only in "non-standard", sloped positions, afterwards, whenever the machine was turned on/woken up. This was all easily fixable by putting my MBP to sleep for a few seconds, once it got a little bit warm.
As time passed, the problems and the sound the faulty fan generated worsened.
At some point, I wasn't even able to get the noise away by "slamming" my notebook (though of course as gently as possible) onto the table, or putting it to sleep over and over again.
Also, the noise was getting more and more grinding. At some point, people mistook my Notebook for a truck.
To get things cool again, I decided to replace the faulty fan.
Pretty straightforward here.
I bought the necessary tools and followed the guide.
Afterwards, I took the time and cleaned the other fan as well.
It's just a fan... you'll figure getting it in and out eventually. Be careful with the mainboard connectors.
Phillips #00 Screwdriver
TR6 Torx Security Screwdriver
MacBook Pro 15" (Late 2008-Mid 2012 excluding Mid 2009 2.53 GHz) Right Fan