Very loud slow fan.

[InterwebsMC]

Recently, my computer has randomly been getting really loud for about 5 minutes, and then slowly returning to normal. Even more recently, it has been happening with increasing frequency, and now it is constant. Here is what I know so far:
1) It is the fan at the back of my computer.
2) When it gets loud, it gets really slow as well.
3) HWMonitor says it is at 0 to 675000 RPM during this time.

I would really appreciate some help, as I need a quiet computer.

 

[marwan051]

It's actually a chain reaction, if your probably CPU get's hot from gaming or other power demanding processes the fan will go on to cool it down, the louder the fan the hotter your CPU. If your fan is spinning at it's fastes RPM and your pc's lagging your fan can't handle the heat but there is also a great the cooling paste isn't applied very well,

 

[InterwebsMC]

It's actually a chain reaction, if your probably CPU get's hot from gaming or other power demanding processes the fan will go on to cool it down, the louder the fan the hotter your CPU. If your fan is spinning at it's fastes RPM and your pc's lagging your fan can't handle the heat but there is also a great the cooling paste isn't applied very well,

This happens while idle. And I have a pretty great PC, so I don't think it is lagging.