There are various components that are dedicated to creating a PC that's as quiet as possible, here are some of the options.
One of the best ways to keep noise down in your system is to work preventatively. Although it's possible to locate and eliminate excess noise once you've got a PC you want, it's preferable to build a PC that has quietness in mind from day one. Everything from PSUs to hard drives are available with 'silent' variants that make less noise than a standard version, though they usually trade off something in terms of price or performance to do so. The upshot is that no silent PC will ever be the fastest you can get for your money - but if you're sensitive to the noise your PC makes, it'll definitely be the least irritating.
So, if you're looking to choose some quiet components for your next PC build, this guide has everything you need to make the right decision.
Hard Drives
Afthough SSDs are the only way to get a completely silent hard drive due to the complete absence of moving parts, there are reduced-noise mechanical drives available. For example, you could go for a hybrid SSD/HDD drive. Hybrid drives have suffered from a bad reputation because the earliest models had an almost inconsequential amount of flash memory and they were quite unreliable, but modern varieties are actually not terrible and might be worth considering if you want a reduced-noise storage solution.
In a hybrid drive, the integrated flash memory allows the unit to cache regularly used files onto noiseless SSD memory. This means some data can be read repeatedly without the drive heads having to move more than once, which means no additional noise is generated. They can also use the SSD to pre-read data that your system might soon need, which means that the platters have to spin up to their highest speeds less often because the data that would be read has already been cached.
For around £150, you can buy a 4TB Seagate Hybrid drive with 8GB of flash storage, which is as big a hard drive as most users will ever need. Cheaper models with less storage are available, and it's also possible to buy hybrid drives from other manufacturers like Western Digital and Toshiba.
It's worth pointing out that the noise reduction you'll see from a hybrid SSD is only small - you'd achieve a better reduction in sound by putting a normal hard drive into a drive enclosure, which would also cost a little less in the long term, particularly because you could re-use the enclosure. However, if you don't have the space for a drive enclosure and can't afford a full-size SSD, this is one option.
Another alternative to buying hybrid drives is just to get a low-power drive instead. Low power drives are designed to save energy, which means that they have a slower spindle speed (5400rpm instead of 7200rpm). Since one of the things that causes noise in hard drives is the vibration caused by a fast spindle, slower ones are quieter. Of course, a slower spindle also means that access times are longer, which can be off-putting. Mechanical drives already create a huge bottleneck for most PCs, so tightening that even further isn't necessarily desirable, especially on a primary drive.
Still, low power drives do have the benefit of costing slightly less than their line-mates. Western Digital's Green drives are tuned for energy efficiency and specifically aimed at low-noise and low-heat uses, and cost £10-£20 less than the WD Black and WD Red varieties. If you want a quiet hard drive, they're certainly an option worth considering. They're not all that green, mind you; one estimate showed that in a year of average use you'd save about £5 of energy - but they are definitely quieter, and that's what we care about.
Graphics Cards
If you're a gamer with a high-end system you're probably used to dealing with fan noise (or, at the very least, you've bought a pair of headphones to block it out). Graphics cards, by their nature, introduce a lot of heat into a system and when they're running at full pelt the fans have no choice but to kick into high gear, which makes PCs the noisiest just when you want to be concentrating on something else.
Assuming that you actually want to play games and therefore can't make do with an on-board GPU, there are a few options available to you. Fanless graphics cards do exist, replacing the normal cooling with a large heatsink. This means the card is capable of dispersing enough heat that the GPU can work to full load even without a fan, but it does come with some drawbacks. Fanless cards are around £10-£30 more expensive than the aircooled versions, partly because they require a high-fidelity GPU, and partly because they're just not popular enough for economy of scale to reduce their price.
They also tend to be mid-range cards. At the high end of the market, where two or even three fans are required to cool a GPU, a heatsink alone wouldn't be able to compensate for the high temperature. This also means it's inadvisable to overclock a heatsink-cooled graphics card, because the tolerances are much lower.
Still, if you want to buy one there are a few models available. So few, in fact, that we can list virtually all of them in order of performance. To avoid going too far back we've excluded models with DDR2 RAM on the basis that they're out of date - all of the cards listed below use either DDR3 or GDDR5 memory. Note too that only the specified models are fanless. Some of the 1GB cards listed also come in 2GB varieties which use cooling fans instead of the heatsink.
The Asus and MSI GeForce 210 cards are the cheapest, at around £20, but they're essentially old stock designed for systems that don't have an on-board GPU, and perform little better than one. Indeed, they're considerably worse than those you'll find bolted to any CPU released in the last few years. The FHIS Radeon HD 5450 Silence (1GB), XFX Radeon HD 5450 1GB MSI AMD Radeon HD 5450 1GB are next cheapest, priced around £30, but still only perform as well as Intel HD Graphics 3000 as found on an Ivy Bridge CPU.
A slightly better and similarly priced card, the GT520 is a little slower than Haswell's on-board GPU, the Intel Graphics HD 4000. In the current market you're more likely to find it being sold under its redesignation of the GeForce GT610. Asus sell it as a fanless model in both 1GB and 2GB varieties, while Zotac sells just the 1GB version.
The GeForce GT630 costs around £40, and can be bought in 1GB fanless form from Asus and in a 2GB low-profile form from Zotac.
Getting towards the higher end of the market, Asus' most powerful fanless card is the 2GB GT640 DirectCU Silent, which it sells for £70 and is as powerful as a GeForce GT740 or a Radeon HD 7730. The 1GB Sapphire Radeon HD6670 Ultimate is also equivalent to the GT 640, but it's near-impossible to find new at retail price now that it's several years old.
However, it's worth pointing out here that EVGA also sells a 2GB fanless GeForce GT 720, which is about as powerful as the GT 640 and HD6670, but uses the latest chip architecture and is much cheaper - just £45. Don't be fooled by Zotec's fanless 1GB GT730, however - despite the higher model number, the GPU in that is actually a rebadged GT620, which is itself a rebadged GT530 and therefore much less powerful than the hardware designation suggests.
In the end, though, the most powerful fanless GPU you can buy is the Radeon R7 250, which is sold in 1GB form by both XFX and Sapphire for around £75 - somewhere in the region of £15-£20 more than the air-cooled version. That said, as far as we can tell, XFX's version of the Radeon R7 250 appears to be out of production these days, making pricing very uneven - and thus the Sapphire version is probably your best bet. The full model name is the Sapphire R7 250 Ultimate, and it's easily to pick one up by scouring some of the familiar component retailers, including eBuyer, Scan and CCL.
All that said, silent graphics card isn't your only option for a quieter graphics card. You can also buy VGA coolers which, for anywhere between £25 and £65, will add a pair of extra fans or even liquid cooling to your graphics card. They're not perfect -they tend to be bulky and hard to install - but they do work.
We admit that it might sound counter-intuitive that you can silence your graphics card by adding fans to it, but it's simple, really - more fans mean less work for each fan, which means less noise. Spreading out the cooling effect also increases its efficiency, meaning the temperature stays lower overall. If you want to keep hold of a high-end card and reduce noise, this might be your best option - and probably your only real one.
Power Supply Units
To buy a quiet PSU, you need to look, primarily, for efficiency. The worse a PSU is, the more energy it loses to heat. This is dictated by many different things, from build quality to QA processes to the raw materials used, but ultimately it all adds up to one thing: quiet PSUs are pricey. A good value PSU will tend to have 'quiet' fans, rather than completely silent ones. They may use liquid rather than ball bearings which reduces friction and vibration, and where possible the fans are larger so that they can run slower. However, if you've got cash to spare you can also investigate truly fanless PSUs, which are so efficient that they can safely deactivate their fans during times of low load.
For most people, the best option will be a quieter rather than a silent PSU. The Be Quiet! Pure Power L8 is a 400 watt unit with 88%+ efficiency (Bronze rated) you can pick up for around £40 - only £15-£20 more expensive than a generic low-end PSU, and it's strong enough to power any average system - though it might struggle if you're planning to run a high-end graphics card or something similarly draining.
If you're running a slightly more powerful system and need a PSU with a higher wattage, something along the lines of the FSP Raider 550W Quiet PSU might make sense. For £50 you get a bronze-rated PSU with a variable-speed 120mm fan, and it's got the wattage to run the latest hardware. Multi-GPU systems might still struggle, but for the most part it'll handle anything you throw at it.
At the absolute high-end, we like Thermaltake's PSUs and the Thermaltake Paris is a 650 watt PSU with a reliably quiet 140mm fan, 80 Plus Gold efficiency rating and fully modular cables. At £95 it's towards the higher end of the pricing spectrum for PSUs, but it's not excessively priced for a quiet one.
For truly silent performance, your options aren't any more limited -just a bit more expensive. The 300 watt SilverStone SST-ST30SF Strider has an 80mm fan that deactivates when the PSU temperature is low enough - something non-specialist PSUs don't do. It costs around £42, which is high given the low wattage it can output, but bronze efficiency rating means most of that wattage is usable by the system. It'd be ideal for a HTPC or low-use desktop.
For systems with greater power demands than that, you'll struggle to find better than the FSP Aurum Xilencer AU-500FL, which can output 500 watts but has absolutely no fan. Obviously, it's expensive compared to other 500W PSUs - in fact, at £150 it's more than three times as costly as an average model - but you won't find a fanless PSU with a better output than this. As well as 80 Plus Gold certification, it has fully modular mesh-sleeved cables with Velcro cable management. You could easily power a mid-range gaming system off it, though take care if you're building up your system - 500 watts goes less far in reality than it does on paper. Unfortunately, there are no shortcuts to cooling PSUs. If your current one is too noisy, your only real option is to replace it or try to tackle the general temperature of your PC. Cleaning the PSU out might help, and adding an extractor fan to your system might decrease the temperature of the air the PSU sucks in - but in this case, the best way to see results is to spend money.