I have five OptiPlex GX620s and two OptiPlex 745s.  When the hard drive in one of the 745s died a few weeks back, when I was removing the drive I observed that it was extremely hot to the touch.  I suspect that this heat served to shorten the life of the drive.

After that happened, I installed SpeedFan to monitor the temperatures of all of the OptiPlex's hard drives.  What I discovered was that two of them run hot (54 C), and a third runs VERY hot every single day (up to 58 C).  Another thing I noticed is that on computers that don't run hot, their cooling exhaust fans run high far more frequently.  You can't so much as run an antivirus scan without the fan kicking into high gear.  On the other hand, on the hot computers, the fans rarely (if ever) sound like they're running at high speed. 

I've run diagnostics to confirm that they can run at high speed, but it seems to me that whatever triggers this behavior is not working properly.  Maybe it's a temperature sensor.  Maybe it's something else.  But I'm concerned that the hard drives' in these computers days are numbered.  I'd really like to get this resolved.