Crash makes a good suggestion... Dells are usually very quiet.
But there may also be some things you can do to quiet down your existing case...
1) Get that heavy rough surfaced self-stick vinyl they use on bathroom windows (most hardware stores have it) and line the sides, top and bottom of your case with it. Be careful not to block cooling vents...
2) Put 10 ohm 5 watt resistors (widely available in electronics stores) in series with the power leads of your fans. This only knocks about 5 to 10% off the speed of the fan and has a minimal effect on cooling, but it does quiet them down rather noticeably.
3) Shock mount your Disk drives. I line the disk bays with two layers of vinyl electrical tape before installing dives. This minimizes vibration of metal against metal and can sometimes quiet a drive down a fair bit.
4) Shock mount your fans. Cut small washers made out of bicycle inner tubes (or similar rubber) and put them between the fan and the case and between the head of the bolt and the case. Again, this minimizes vibrations being transmitted through the case.
4) Increase air intakes... not by adding fans, but by enlargening the air intake openings at the front and bottom of your case. Fans run quietest when they aren't creating a vaccuum.
5) Cut down on the number of fans. With good airflow you should only need one fan in the power supply and one case fan for adequate ventilation on an average system.
6) Cover unused exhaust fan openings. I make flat squares, the size of fans out of plastic and bolt them in through the pre-drilled holes. If you have good air intake at the front, this can actually lower case temperatures and it blocks sound from travelling out the open holes.
7) Place air deflectors on the output vents (where your fans are), a simple home-made cardboard cube with the back and bottom cut out, taped over the fan openings should suffice. This deflects sound downward and away from the rest of the room.
8) Wear ear plugs
Hope this helps...
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