Most PCs, including laptops, are quiet some are almost silent. When the start making a lot of noise it normally means that the PC is overheating and the internal fans are trying to cool the PC to it's optimum temperature which for a desktop should be less than 50 degrees C.
All PCs contain one or more Fans. Each fan is connected by a sensor cable to the Motherboard and the temperature is of the system is controlled by how fast the fans are 'spinning' many fans can spin well in excess of 3000 rpm if your fan is spinning at 3000 rpm then your system is going to be noisy and it generally indicates that the PC fans are obstructed in some way and the PC is not being cooled effectively. This usually this is caused by the build up of dust in the PC and around the CPU heatsink and/or CPU fan.
It just got worse as I began to remove the components.
On the left is the inside view before, note the black fan which is almost completely clogged which is one of the reasons the PC is noisy the fan is struggling to draw air through the system. On the right is the case after cleaning - not that I remove every component and clean it this includes the CPU heatsink see next pictures.
The heatsink was completely blocks with fine dust. This caused the fan to spin as fast as it could as enough heat was not being 'drawn' through the heatsink to cool the CPU which resulted in the PC shutting down after it had been on ~30/40 minutes.
A further important point to note is that whenever you remove a CPU heatsink you MUST replace the thermal paste (the grey gunk) still visible on the bottom of the CPU heatsink in the above 'photo which acts as a heat transfer agent between the CPU and the heatsink. If this is not done the CPU will fail catastrophically and permanently in a matter of days.
Once the fan was cleaned, thermal paste applied, all components reseated and tested the PC worked fine and was so quiet compared to how it was brought to me. I quite enjoyed repairing as it was interesting to do and a bit of a challege.
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