[CentOS] Something is writing a log

I can just be sittting, doing nothing, and I hear the sound of my 
hardrive head moving.  Just every so often.  Like some process is 
writing a log.

I have looked in /var/log and do see occational updates to acpi and 
messages, but that does not account for all the clicks.

Is there somewhere else to look for logs?  I would really like to know 
what process has something to remember.....