Unless you've switched to a liquid cooling system in your PC, the loudest component probably wouldn't be the hard drive, it'd be your fans. But if you have, then these NB-X-Swing hard drive silencers could be just the thing to keep you throwing your dog out of a window over drive noise.
How does this work? You screw your hard disk into the swings, mount it into an empty 5 1/4" bay, and fire up your PC. By cushioning the contact between your disk and your case, the X-Swing takes out (from xsreviews' test) all the noise generated by vibrations. You can still hear the disk spinning—it's not meant to stop that—but everything else is dead silent.