Well as far as I know, it's hard to diagnose HD problems with tests. Problems with accuracy and such, but I'm not really an expert with HDs. If you heard a whizzing noise while playing a game and downloading a file, my first guess would be that it was the CPU fan, or the video card fan. They can do that sometimes, I would check to see where the sound is coming from the next time it happens.
Even though you were using two different partitions, from what you've said you are still only using 1 hard drive. In this case, it doesn't matter that you were using separate partitions, you're still putting the load on the same physical drive.