Hrm. You may want to see if you can use a CD version of Ad-Aware and run it...you may have too many registry files in the registry.
If it is making a click sound every second or so, your HD is fried.
Also, turn it off and let it sit for about 5 minutes, sounds silly, but it has worked for me.
Good luck.
I have turned it off and on a couple of times on the clean-the-brain theory.
It is pinging, like an annoying modern alarm clock.
Have you ever run into this before?