Do you really need to put up with all that noise just for 9gb of hard drive space? With the price hard drives are now, you can get 20x that space for quite cheap, or just remove it...
Try taking a bunch of elastic bands and suspending your hard drive in midair so that it's decoupled from the case. Most of the sound comes from the vibration of the hard drive shaking the entire case, if you remove the tight connection, it'll be quiter.