How can I replace the cooling fan?

My first PBG4 Titanium died this past August, and I replaced it with another one in September. About six weeks ago, the "new" machine's cooling fan stopped working. Although I was able to get it to work for a couple of hours one day, I haven't been able to get it to work again.

I'm guessing the fan has died, as it sounded like a coffee grinder in the days before it apparently died. To the best of my knowledge, the cooling fan in the otherwise dead first machine is known to have been working when the logic board died. Is it possible to swap the cooling fans?