Thank you for the response. The click sounds like it's coming from the left side, of the bottom half of the laptop, under the surface, or under where my left wrist is positioned when I am typing. It's possible I'm hearing it through the speaker on the left. I was trying to time the clicks, but ran out of patience after 4 minutes. Is there anything I can do to trouble shoot it? Thanks-
If it's not the original PowerBook, and you have the original OS X disks that came with your PowerBook, run the Apple Hardware Test. If it's the first PowerBook, the Apple Hardware Test is available online.
When prompted, run the extended test. Depending on how much memory you have in the system, the test can take an hour or more.
TechTool Deluxe or Pro can do similar testing, too.
You're looking to see if it gives you any error messages about the hardware in your system.