You need to open the case.
Look at the fan. It may be dusty. That dust can cause vibrations. Using an artist brush, gently clean the fan. Using a can of compressed air, blow away any dust on the heat sink.
If it's still make to much noise. Get a new fan that have the same dimentions. Larger may not fit, and smaller won't do the job.
Electro, April 2013
