Why does my hard drive fan run so fast???

[Freqflyer30]

My fan has been going on faster and then shutting off frequently while I'm on.  It recently started going on twice as fast and then only slowing down.  Now it seems to always be on.  I have two drives in my pc.  Drive C has the Windows XP OS on it.  But Drive D is 110 gigs and has all my files and pictures on it.  What should I do to shut that *censored* fan up??

[GX1_Man]

Hard drive fan? Is this an add-on? If so, what brand name?

If this is not a hard drive fan, what kind of fan is it? I have never needed such a thing. What exactly makes it speed up or slow down? (Your post was not clear.)

[Freqflyer30]

Maybe I'm wrong.  Its the fan on the back of my pc.  It speeds up then slows down alot.  Is that a problem?  Because it didn't do that before and my pc has slowed down alot.

[Siscorskiy]

....exhaust fan?

[Freqflyer30]

Yeah thats it.

[GX1_Man]

Or power supply fan? Do you know how to check your system temps? What kind of machine is this?