A well designed case will help
reduce the amount of noise that escapes from fans and hard drives that are
inside. SVC recommends several different cases that have known to produce very
quiet PC's when built correctly. There are plenty of other cases that could be
turned into silent PC's as well, but we have listed just a few to give you a
good starting point on what kind of case to look for. There are several simple
factors when it comes to noise reduction.
Construction and Material
A sturdy and thick case will resonate less than a flimsy and thin case. That is
why there are no full aluminum cases listed in this section. Steel cases are
heavier, which can cause a problem those who lug their case around a lot, but
they contain noise a lot better than lightweight cases. Construction will also
help eliminate resonating. A case with support rails and solid construction will
generally give off a little less noise than poorly made cases.
Fan Compatibility
One thing a quiet case should have are 120mm fan holes. Larger fans are able to
move more air without producing as much noise as smaller fans. For example, for
a 80mm fan to move 39 CFM of air, it creates about 32 decibels of noise. A 120mm
fan would only create 25 decibels to move the same amount of air. That is why
larger fans are key to creating stable and silent systems.
Ventilation
How much ventilation a quiet case should have a debatable. The more proper
ventilation the case has, the less fans it will need. However, the more openings
a case has, the more noise it will allow to escape. Regardless of how quiet you
need your case to be, you will need proper ventilation designs to efficiently
cool your case.
Quiet Cases 
