How to make your PC quiet
Run silent, run deep
It's possible to make no compromise on performance and yet still have a quiet PC. There are a wide range of products available to control PC noise, most of them offered as user-installable upgrades. But do bear in mind that if you are building your PC yourself you could invalidate the warranty on several parts by modifying whatever cooling systems they ship with or replacing any of their parts.
More importantly, when working with some of the specialist products you will invariably have a learning curve to make during which time you may damage some of these products or the PC components they are fitted to. Do read the products' manuals carefully, browse through their user forums, and do stick to the book when fitting and using these products.
There are some cases designed to be quiet and marketed on that claim. Using a search engine for terms like "quiet cases" or "no noise cases" should point you in the right direction. Some of these cases are built like huge heat-sinks and use clever technology that will allow you to dispense with the use of all fans inside the PC. There are other, cheaper cases that have an acoustic lining that muffles some of the internal sounds. Either way, having a quality case makes a lot of difference. Case vibration is one of the most common and easily resolved causes of PC noise.
A variety of acoustic lining products are available. Some of them are basic sheets of foam, others are dual-layer products with a thicker barrier material under a layer of sound absorbing foam. These lining products usually have self-adhesive backing. You can cut the sheets to fit along the inside of your case, peel the back off and fit them yourself. Some acoustic lining products are as little as 3mm in thickness, others as much as 10-15mm. If space is restricted in your case you may want to go for the thinner (but less effective) products.
There are some cheap bitumen based products that degrade quickly over time and can be quite risky. If your PC relies extensively on the case body to dissipate heat - as is common with many aluminium cases - then you may want to create some additional airflow to compensate for the reduced cooling. You can do this via extra chassis fans.
A variety of specialist fan manufacturers make low-noise heat sink and fan combinations for processors. These involve using copper contacts the better to transfer heat from the processor to the heat sink, using large heat sinks to quickly dissipate that heat to the air above the processor, and using large, low-noise fans to move the heated air away from the processor. What's a good fan noise rating? Under 30dB is usually considered quiet.
The problem with larger heat sinks is that they don't fit in all cases and are particularly unsuitable for low-profile desktop cases. Very often the location and size of your processor makes it impossible to fit one of these heat sinks. Furthermore, in dual-processor rigs, you may find that your CPUs are too close together to be able to use these (generally) quite wide heat sinks.
This has been gaining popularity despite the obvious downsides of combining water and electricity. Liquid absorbs and transfers heat more effectively than air does, so there's a practical argument in favour of piping water over the CPU instead of air.
Some cases manufacturers now provide the water cooling kits as options with some of their cases, and one or two others offer water cooling kits integrated into some of their larger cases saving you the unsightly mess of having a pump and tubes on your table top. In either case though you will need to have an external radiator unit that dispels the heat.
The problem with water, of course, is that unlike air-cooled systems, water needs to be enclosed. And it needs to stay enclosed - with no leaks - or it will damage the electronic components in your PC. This makes for equipment that is both bulky and expensive.
Peltier coolers and other heat exchange systems have been tried in PCs with limited success. Condensation can cause problems, and you need your heat output to be constant. If your PC isn't under constant, even use or you have energy-saving features that trigger system sleep modes, you can't use a Peltier cooler. That excludes most PCs. Thermoelectric engineers have experimented with turning heat into electricity in a variety of other ways but most methods require large amounts of heat - about 200-300 degrees C - and even then only about 20 per cent of the heat is converted to electricity. Other thermoelectric solutions consume a lot of power and/or generate substantial heat themselves and require active cooling.