CPU fans usually start whining after two years.
You shouldnt have any problem replacing it, the old fan will pop off and probably not leave much residue from the thermal waffer on the CPU. Scrape it off with a razor blade if you want.
Most of the CPU fans come with a thermal waffer that is equivelient to the thermal paste that everyone use to use.
If you really want real good thermal transfer between the CPU and the fan, you would scrape off the waffer on the new cpu fan, and likewise any residue onthe CPU and then you would use a thermal heatsink compound like Artic Silver. Apply a thin layer to the CPU and then slap on the CPU fan. Don't forget to plug it in.
A little bit of that Arctic Silver goes a long way, you'll see what I mean if you get some on your clothes
