I had an Acer TravelMate 4270 with a noisy fan. Here's how I fixed it.
1. Unplug the laptop and remove the battery
2. Open up the laptop at the back. Disconnect the fan and unscrew the cooling unit.
3. Unscrew and remove the fan from the cooling unit.
4. Thouroughly clean the cooling vents of the cooling unit making sure its free of any dust.
5. Replace the laptop fan with a new one if necessary. The bearing of my fan was worn so I changed it. I found a replacement online.
6.Remove the old thermal paste on the cooler CPU and CPU.
7. Apply a thin layer of new thermal paste to the cooling unit, and screw it down.
8. Take it off again and remove the excess thermal paste from the cooling unit. You should be left with a thin layer of thermal paste on the CPU and GPU.
9. Screw the unit back into place, and attach the CPU fan.
10. Close the laptop back up.
This worked for me, and I think this is the proper way of fixing this problem.
LJ
October 2011