If you have noisey hard drives, try this neat tip and it will isolate most of the hard drives noise from your computer.
Look for rubber dampeners, linerless rubber splice tape or rubber washers. Use a dime as a stencil to outline the hard drive screws and install them before or after the hard drive screws to create a cushion. If you do everything correctly, everytime the hard drive is operating, it's vibration should be absorbed by these new gaskets.