Hope the experts can also include guidelines on:
- how to bring down noise levels of PCs
- cooling options, esp. those that do not make the units more noisy
TIA
- user less and larger fans. a 120mm make less noise but will move the same air as 2 80mm fans.
- use fan controllers and temp monitors. you can monitor and adjust the fan speeds to lessen sound
- user tower type/heatsink CPU coolers than have larger fans. (zalman, arctic, thermaltake, etc.)
- use software that can monitor and change CPU fan speeds (or CPUs that adjust their own temp)
- proper internal wiring for more efficient airflow which makes efficient cooling
- change GPU fans to 0-noise heatsinks such as Zalman (there are cards that are already 0-noise out of the box)
- use noise absorbing material (though this could raise your temps since the case will radiate less heat)
- use low noise Power Supplies with larger or no fans
- efficient fan placements (blow holes, rear, side) depending on the case, placement of case, etc.
I hope this helps!