First - you might get more traffic if this was in
Genius Bar.
However, can you tell us a bit more please...
How many apps are running at once?
When was the last time you either restarted the machine, repaired the permissions or in general gave the machine a "clean start"?
How much space do you actually have available on your HD?
I would have guessed that it had something to do with paging out. My 20GB HD used to click away incessantly, especially when I only had about 1GB or less of space available on it! Finally, though, I bought an external FW drive and archived a lot of my files and data. This then cleared up my HD space and I'm happy to say that the clicking noise from my HD is almost a non-event these days!
