(continued from above)
First, try a free software fix. Many newer hard drives offer different performance levels that let you balance performance and noise: For example, if you give up a little "seek" speed you may greatly reduce the chattering noise the drive heads make. (Some drive vendors refer to this as "Acoustic Management," but other terms may be used.) Drive vendors and motherboard vendors may offer software to access and control such drive features, and it’s often free. For example, see Intel’s software at http://www.langa.com/newsletters/2003/2003-01-30.htm#4 , or see a general tool from Hitachi (also free) that can work on a very wide range of drive brands and models: http://www.langa.com/newsletters/2003/2003-02-10.htm#3 .
If the software fix doesn’t work, some very, very simple hardware fixes may help:
Open the PC (powered off; all normal cautions apply), and gently remove the hard drive from its bay or mount. This may require loosening a few screws and unplugging two cables, but it’s all very basic Erector-Set type assembly, maybe with a little Lego-like plugging thrown in: No special knowledge or tools are needed.
Reattach the cables and temporarily prop the drive in the case (perhaps resting on the case bottom) 90 degrees from its original orientation. That is, if the drive had been horizontal, securely prop it vertically. If it had been vertical, securely place it horizontally. Make sure nothing touches the circuit board on the drive.
Now power up the PC. You may find that the drive is much quieter in this new orientation, especially if it’s older and has some mileage on it. (The bearings may have worn in a set orientation; moving the drive may present fresh wear surfaces, and/or redistribute the lubricant.) If the drive is a lot quieter, you might want to look at permanently mounting the drive in the new orientation.
Second, turn the PC off and wait for the drive to spin down. Gently place the drive on a piece of foam or other cushioning material so that no part of it touches the PC’s case. Start it up again and see if the sound is significantly different. If it is, then all you may need is some kind of cushion to prevent the drive’s mechanical noises from conducting through the PC’s metal case. For instance, you may be able to use very small rubber O-rings as cushioning washers around the drive’s mounting screws. (You can buy O-rings at almost any hardware store for a few pennies.) Or perhaps you can think of some other mount-cushioning option that will serve the same purpose. Use your imagination! Just don’t reduce airflow around the drive, or you may cause heat buildup.