PC Fan Repair
Problem: PC starts making a strange noise.
Hardware: Fan (both in the power supply and on the CPU).
Resolution Steps: Strange noises coming from the computer are usually caused either by a fan or the hard drive (this isn't too surprising really, these are the two most mechanical parts in the box!). Another possible cause is the CD-ROM drive (either a CD rattling on the tray or the whole tray rattling loose), but this is far rarer.
The first step is to find out which device is making the noise. Remove the computer case's cover and listen carefully. You should be able to pinpoint where the noise is coming from (unless it's one of those intermittent faults that always seem to disappear when the technician arrives to fix the problem!). Because you're working inside the PC you might want to wear an anti-static strap for protection against static electricity.
If the noise appears to be coming from the hard drive then you can confirm this by turning off the PC, unplugging the power plug from the hard drive and restarting the PC. If the noise isn't heard then you can be pretty sure that the hard drive is the culprit. There's not much you can do about a noisy hard drive, often it's a sign that the hard drive is on its way out and you should replace it immediately while you can still retrieve data from it.
If the noise appears to be coming from the fan over the CPU then you can confirm this by carefully sticking a paper clip or small screw driver into the fan's blades and seeing if the noise stops (this sounds rather drastic but it will tell you straight away if it's the fan or not). Don't stop the fan for too long, a second or two is all it takes to see if the noise stops.
It's usually fairly simple to see if the noise is coming from the fan in the power supply as it's easy to get your ear close to this fan.
Now that you know it's a fan problem you have to decide if you want to replace the fan or try to repair it. If the PC is still under warranty then go for the replacement option (after all, it won't cost you anything). If the faulty fan is on a slot-type CPU (i.e. the CPU and fan are built into a thick board that sticks up from the motherboard) then I'd opt for replacement. If the problem fan is in the power supply and you're not confident with electrical safety issues then opt for getting it repaired or replaced professionally. If you want to try repairing the fan yourself then read on...
If the CPU is a socket type then remove the fan. Removal is usually accomplished by either unclipping a metal clip or two or by unscrewing four screws. Sometimes the fan and heatsink are one unit, other times they are separate (in which case leave the heatsink on the CPU and remove just the fan). Before removing the fan take a note of the sticker on it so that you can replace the fan the right way up.
If it's a slot-type CPU then you will have to remove the whole CPU board (look for a plastic clip at each end of the board).
If it's the power supply fan that is causing the problem then carefully remove the PSU box (this is usually achieved by removing four screws from the back of the case that attach the PSU to the case). Depending on the style of case and the length of the power cables you might be able to lift the PSU box up and rest it on the case, or you may have to disconnect some or all of the power cables in order to be able to lift the PSU box out. Remove a couple more screws and you should find the PSU box comes apart. Take a note of which way round the fan is so you can replace it correctly and remove the four screws holding the fan in place and lift the fan out (you may have to unplug it first).
We're going to add a little oil to the fan so make sure you've got some handy (use general purpose oil, i.e. sewing machine oil). The next job is to locate where to put the oil. You will usually see a sticker in the centre of the fan. Carefully lift the sticker up. If you see solid plastic in the centre of the fan then try the other side of the fan. In the centre of the fan you might see either a hole with a spindle in it, or a small rubber cap that you can prise off to reveal the hole and spindle.
Put two drops of oil in the hole and spin the fan around a few times to work the oil in. If there was a rubber cap then replace it. Put the fan back (you did take a note of which way up the fan was before you removed it, didn't you?) Usually fans blow down onto the heatsink and CPU, so it's important you replace the fan the correct way up.
In conclusion, there are two types of fans in use: ball bearing and sleeve bearing. Ball bearing fans are generally better as they last longer. If you elected to replace the fan then try and get a ball bearing sort (they may cost a little bit more but they're worth it). If you tried to repair the fan by adding a couple of drops of oil then you should know that this fix will usually only work for a few months before the fan starts getting noisy again.