For what its worth,

On a laptop I was finding that the disk would spin up approx every 15
seconds.  Some pokeing around found the culprit....

Turned out that squid (yes on a laptop :-) probes one of its cache
directories every 15 seconds.  Now with 16 first  level and 256 second
level directories being used to construct the cache, some quick math
suggests:

	16 * 256 * 8k(block size)
	= ~32mb

And squid was very slowly working its way through this, each time a new
directory was read it missed in the buffer cache :-(.  Tweeking squid's
config to reduce the number of directories fixed the problem.

Perhaps something to add to the APM notes.

	enjoy,
		Andrew