Interesting post from TUAW:
"Wheels said 7:00PM on 8-10-2009
The problem seems to be focused on MacBooks with 7,200RPM hard drives.
If you delve a little further, however, and go into places such as non-Apple Apple product forums. where you can read from people such as Mac Mini modders, the clicking issue enters their domain as soon as they put a 7,200RPM drive into their Mini.
Then you can delve a little further and read that, yes, 5,400RPM drives experience this parking issue, too, only the majority of those drives are apparently so quiet that nobody can tell it's happening. That is, they can't tell until they run a SMART hard drive utility and see that their head parks are WAY out of line with the amount of time that their hard drive has been powered, sometimes MILLIONS of times vs. a couple thousand hours, and you realize something bigger is up.
http://www.123macmini.com/forums/vi...&start=0&sid=b063c7deca1a2cad1463a0c9a4a83644
http://www.dslreports.com/forum/r21566852-WD2500BEVE-in-PPC-Mini-High-Load-Cycle-Count
Then, as you're sitting there, cogitating all this, listening to the hard drive in your PowerMac G4 MDD making little clicking noises (noises you think are normal, since you hear them all the time) and you realize, "HF, this thing's doing too."
This problem, IMHO, is rooted in OS X's Power Management system, and is affecting ALL systems running Leopard. But Vista user's can't rejoice about this, though, since Vista's doing the same thing - Although, from what I can tell, not as badly."