Friends, Romans, Countrymen, give your ears to Silent PCs!
Given the fact that not through engineering limitations but sheer unadulterated cheapness on the part of the manufacturers the vast majority of cables which connect your keyboard, mouse, monitor, and speakers are barely a couple of feet long, most computer users have no choice but to plunk their computer cases on their desks right next to their monitors: a placement which maximizes the transmission of the PC's endless whirring, clicking, buzzing and wailing right into your ear.
For the vast majority of users who aren't incessant DVD and CD swappers, the PC case might as well be in another room. After all, once you've hit the power button, you rarely have to do anything with your computer that can't be done through the input devices. I've had several setups where I've drilled a hole through a wall in order to run the computer cabling into another room or closet. The resultant quiet was a miraculous revelation, as I was finally free of that huge ivory chunk's desk space hogging and most importantly, its incessant infernal noise! Listening to music free from background noise or even just enjoying the quiet immeasurably improved my computing experience, and I heartily recommend it to one and all.
Punching a hole through a wall is not necessarily an option welcomed by most computer users, but there are various ways of keeping the decibel level emanating from your PC case down to a dull roar.
The single greatest offender in any PC case are the fans. Although they are necessary to keep the internal temperatures in your case down to acceptable levels, most fans operate at a racket that sounds like an A380 on takeoff. You can easily replace the fans with identical sized magnetic levitation fans available at most quality computer etailers. These fans lack the ball bearings that the cheaper fans have, thus freeing you from the constant surface to surface grinding and other related groaning that you've accepted as part of the PC auditory environment.
Another place where fans can be replaced are the heat sinks on the CPU and GPU. If you are not an overclocker and are utilizing newer processor units, you can easily substitute their heat sinks noisy fans from hell with oversized fin models which are designed to operate completely passively and with no moving parts.
Don't overlook the Power Supply Unit as many now have three internal fans and they can emanate the screeches of the clatterwheels of Armageddon. Doing your homework to determine which of the many specifically Silent PSUs on the market is the best fit for your requirements will immeasurably aid in reducing your case noise levels. Keep in mind that many Silent PSUs are actually nothing of the sort, so check out the online reviews from authoritative sites like Anandtech before pulling out your credit card.
Silent cases come in all sorts of configurations and price points, some considerably exceeding $500. Mostly they are a waste of money as the noise reduction achieved represents poor value as compared to carefully choosing and matching quality silent components in a conventional case. Many silent cases also unduly restrict air flow leading to some very hot internal temperatures that can fry your components. Generally speaking, silent cases should be avoided.
Take the steps necessary to silence your PC and your ears will thank you for it!