I have a windows 7 box stashed away in my closet, containing (among other things) 2 big HDDs linked together as a mirrored volume - basically a super lazy NAS / media server. I've noticed that when that drive is accessed (whether locally, on the machine itself, or remotely, from another computer, or my xbox, for example) there's a noticeable pause, and then from the computer itself, a 'click!' noise, after which the drive is accessed; e.g. open \\computername\shared\, wait 2 seconds, hear 'click!' and then see files appear in windows explorer.
Any ideas? Otherwise the drive preforms normally - is it a windows thing? a HDD-about-to-die thing? Or a "yeah that always happens, you've just never noticed it before" thing?