I built a computer this week, from components. It has a radiator (for a
CPU cooler) blowing air out the top of the case, so for that reason and
others, the case is a little more open than usual. Usually I choose
"quiet" cases, but I couldn't find one compatible with the radiator I
wanted. The case fans, front and back, are already set to low and I
don't wish to tinker further with them. The case is louder than I expected.

Feeling "desperate", and inspired in the best wreck'ed way, I cut and
taped up the cardboard box the case came in, still cubic-like. I set it
propped up over the case so that there were 2" at the front-bottom for
air intake and 12" of space in front so as to not block the main
"air-take"of the computer (which has a 200mm fan). The top of the box
ended up a foot over the top of the PC (there had been styrofoam in the
container too), and the rear of the case is not blocked at all. The
configuration above has perhaps raised the temperatures 1-degree Celcius
(=2-degrees F). I am running a freely downloadable program called
SpeedFan 4.5 (new to me) which is proving me with no less than 11
temperatures from the components and motherboard to monitor. I could
recommend it to you (get it from the maker to avoid malware. I can get
you a link if you like).

I do not regard the current cardboard box as a permanent fixture. I
am however open to suggestions. I am thinking about going to hardboard.
Is there something I might glue inside to help absorb fan sounds?
Other thoughts? Will its size affect how well it will block sounds? I
will note that if I move so that there is a piece of particle board
between my head and the rear of the fan (120mm), all of the shrillness
"disappears".

BTW, for the disbelievers that are too busy to make them, my cardboard
box does provide me a good "template" from which to proceed. I have to
give the wreck credit for helping me to be creative here! I see I may
need flexibility to make temperature adjustments (to say nothing of
getting at the CD drive, which is not a serious concern). An Easy-lift
on, Easy-lift off solution should suffice. I can put a handle on top! ; )

Thanks for reading!

Bill