using fc3(fedora core 3)! this hdd actvity happens on all the distros i have tried so far!
debian, gentoo, slackware, suse, mandrake, rh9, fc3!!!
you hear the whirring sound the hdd LED comes on then it wont stop for about 10 mins at least!
might it be something like FS check, etc!!!
in any case it happens about every hour