I'm going to try to describe a sound, so bear with me here... This is hard to explain but imagine a piece of tin, and rolling a marble down it, then the marble hitting the ground being the click. Kinda like "whizzz-click, whizzz-click" Don't laugh... If it's accessing the disk like that, I would say get it backed up as soon as possible and get rid of it, as it's probably going bad on you. If it's just clicking like "click click click" then it might not necessarily be going bad on you. Cause if it's just clicking, it could be Windows doing disk indexing, being a pain in the ass, or heavily fragmented as mentioned above in two other posts.
Here's a way see if Windows is acting up on you causing the access, try booting into MS-DOS, or if you're using XP, a really good way to see is to boot into the recovery console and just log on to your installation. Under the console, you'll be talking directly to your HDD, without any of that pesky background operations going. If it's clicking there, even if its making a steady click click click noise, then I'd say it's about to go bad on you. The recovery console is accessed by putting your XP CD in and booting with it. When setup launches, it'll tell you what key to use to get to the recovery console. I cant remember what F key it is, but mash it when it tells you to. The screen will go black with white text. If you're here, your're in the right place.
