Case Fan Slowing Down and Speeding Up Randomly

[Nihren]

I've had a fan on the back of my case since I first built it 4 and a half years ago and it has run at the same speed all this time. However, about two or three weeks ago, it started to slow down considerably at random times. At first it would only last for a few minutes at most and then speed back up again, but now it speeding up and slowing down almost constantly, and it doesn't even speed up that much, just enough that the sound it makes changes ever so slightly.

Before coming here I did do a little googling and someone suggested it might be an issue with the PSU(My PSU is 700w and powers a Core i7-3770 and a GTX 980 Ti among other smaller components. It's the same age as the case fan. In fact, all the parts in my computer, aside from the CPU, GPU, Hard Drive, and RAM are 4 and a half years old.), but I wanted to come here and check before I decide to swap anything out. I have been planning to completely overhaul my computer at some point this year, so the fan itself was going to be replaced eventually anyway, but I don't want to take a part out only to have that not actually be the problem after all. The fan sounds like it's not getting enough power, but I have no idea if that's actually the issue or if it's just dying.

 

[jasonkaler]

tldr: your fan's probably dying.

Long story: a few things come to mind:
1) it could be natural fluctuations in temperature.
2) there could be dirt in the fan or the bearing could be failing.
3) there could be something interfering with the temperature sensor.

point 1 should be easy to monitor with software. see if fan speeds change when temps change.
point 2,3: you could try cleaning the fan but it's better to replace. cleaning them out often only results in a very short term fix.