The biggest foe of the HTPC (home theater PC, that is) is heat.
The second biggest foe is all the noise your system generates getting rid of that heat. Especially if said HTPC is in the room with you when you’re trying to watch a movie.
In my computer, I have no less than six fans running at any one time, and that generates a lot of noticeable noise. Silent solutions like water cooling (which always has me panicked for obvious reasons) are expensive or large. Typically the best way to do quiet cooling with air is to use multiple, large, slow rotation fans instead of one moving quickly, but high-end hardware that’s always on often needs to get rid of large heat spikes quickly, so that’s not always practical.
Enter the Noctua’s NF-F12 integrated noise cancellation fan, which takes a 2500rpm fan and stuffs it into the sound profile of a 1500rpm one, greatly reducing that annoying whine (and this isn’t counting the additional dampening of a case). It does so by emitting noise-canceling white noise straight from the fan itself. Cool, huh?
Product page: Noctua NF-F12