When they're in use, hard drives vibrate, and that means they can get noisy—unless they have the right shock absorbers. In an oldie-but-goodie article, the folks at the Silent PC Review rigged up a hard drive bay with thick elastic bands they picked up at the local crafts store. The resulting setup suspends the drives in space with the elastic, which absorbs vibrations and gives the drives plenty of breathing room. Writer Mike Chin says:
As a simple test, when I touch the drive while it was running, I can feel a fair amount of vibration. But when I touch touch the case right next to the hard drive—or any part of the case, there is NO vibration from the drive. None at all.
When I showed one of my suspended drive systems to my favourite local dealer, it was the complete absence of vibration in the case that amazed them the most. They could not tell when the PC was turned on by the usual vibration of the case. They found it eerie.
You can also use a small piece of rubber in between the drive and its case to quiet things down.