• Steel cases are quiter than aluminum ones, because the denser material
vibrates less easily.
• Quiet cases are available, containing noise-damping acoustic foam. There
are 3rd-party acoustic foams that you may decide to add as well.
• Experiment with rubber or foam washers when mounting drives and fans.
These will dampen any vibration these devices cause.
• Keep cables tied up and neat. Not only will this keep them clear of fans
(which could quickly cause dangerous heat build-up), but the reduced
impedence of airflow throughout your case will make things cooler. Flat,
ribbon-shaped cables can safely be folded up to a fraction of their original
width.
• Make sure your case has rubber or foam feet if it rests on a hard surface.
Placing it on carpeting will also reduce vibrations.
• Underclocking will reduce system performance, but you can also then reduce
the CPU voltage, and power consumption as a whole. Noisy fans may
then also be operated at reduced speed or eliminated altogether, as the
computer will produce less heat. The converse of the diminishing-returns
law for overclocking is that underclocking can prove surprisingly effective.
• The really obvious, but surprisingly effective: keep the computer under
your desk or even in a closed cupboard, rather than under or beside your
monitor.
NOTE: No matter what technique you use to quiet the machine, be sure to
keep a steady supply of fresh air over all components. Don’t put your machine
in a closed cupboard unless you are sure heat will not be an issue. If you
use acoustic foams, be sure they aren’t acting as insulators, too—and keeping
components hot.