I've had to replace the fans on three of the 17" machines. All started with the left fan going out first. Failure included a very loud screeching noise at the end. On the first one I just replaced the left fan, then two weeks later the right fan failed. On the next two I torn the machines down to the heat sink, cleaned the vents which were about 70% blocked, replaced the thermal paste on the heat sink. That solved the problems and the machines have not been back in. Here's how to replace the left fan: [guide|332] Here's the right fan:[guide|330]
Here's how to get to the heat sink: [guide|336]
Here's a general guide on how to replace the thermal paste. I use Arctic Silver Thermal Paste: [guide|744]