Last night I went to download the update for WoW. Anyway, my hard drive and fan seemed to be spinning very high. Towards the end of the download, I heard a "whirring" or "whistling" sound, which sort of faded in, got a little loud, and then faded out. It did it about 3 different times, but hasn't done it since. Is this an indication that something is wrong with my hard drive? Or could it have been the cooling fan? My first hard drive that crashed would give me a clicking sound, but this was a high-pitched whirr or whistle. Any ideas?

It sounds like you aren't sure what made the sound. It's very hard to say if there is a problem or not if it could have been one thing or another. I have never heard a harddrive make a sound like you described, but that doesn't mean that it can't happen. I have heard optical drives and fans make sounds like that though.

If one of your fans has a variable speed determined by the temperature surrounding the fan (some fans do), then it is possible that the fan just kicked up its speed as needed when the temperature around it increased.