Change out the fan with one just like it. Use the same spec as far as cfm is concerned and DO NOT use a sleeved bearing fan. Only use a ball bearing fan in a PSU. Check BGMicro.com for a good inexpensive fan. Your fan type should be listed in the manufactures specs.
For a tutorial or how too. Google replacing PSU fan, there are many out there with good pics.
...Galvanized