- Turned on my laptop this morning, and it started making a horrible, loud noise - I recognised it from a previous laptop; the fan was definitely playing up

- Hard-closed the lapop, and turned it on again, and it was making the same noise

Suddenly, it came up with "Windows Repair" or something - I just let it do it's own thing because I needed it to turn on properly so I could shut it down

- After the repair was finished, the noise calmed down. I shut it down (installing some updates) and turned it back on again-  no noise. 

- How can "windows repair" (a SOFTWARE thing) fix a HARDWARE issue? Is it actually fixed, or was it just a coincidence? Is my computer alive? How did it know that it had a problem with the fan?

- Help! I need to know if I have to call an exorcist 

Kill it with fire before it starts its conquest over the world.

While I do not know the specifics, it is entirely possible for software to cause hardware to damage. Glitches in driver software may force a component to work too hard and overheat, thus causing your fan to go OTT.

You may have updated a driver which had a glitch, causing a component to overheat, and that update you downloaded was a fix for the glitch. Although this seems unlikely, as the turn around on the bug fix sounds like it was remarkably quick... and software never releases that fast (most firms have rigorous release strategies).

Kill it. Otherwise the machines will rise.

Is it possible that a build up of dust clogged up some of the vents/heat sinks causing a buildup of heat and the faster fan speed simply blew out said dust returning it to normal efficiency?

take the back cover off and get a can of compressed air to remove all the dust, this should fix the problem and stop windows repair from popping up.

you can get cans of compressed air from most computer stores like maplins.

I always thought my laptop was self-aware when it would turn itself on in the middle of the night sometimes, if i would leave it plugged in.

Kill it before it lays eggs

I was expecting something more interesting/bizarre -_-U

FYI Fan speed (in other words, how much noise it makes) is controlled by software, so yeah, nothing really crazy going on here.

Windows Repair started because you hard closed your laptop & had nothing to do with the noise.
Your fan probably just had some dirt that got "cleared" after leaving it spinning during the repair process.

But just to be sure.

FoS: Radish's Laptop