I had a similar problem. Using Disk Inventory X showed me that I had some ASL Log files going crazy. I wiped them all out and the 'problem' was solved.
What I don't know is how or why the log files went crazy (multi GB), but it doesn't seem to be recreating them so I'm keeping an eye on it, but since I didn't make any root cause changes, I'm assuming it's still screwed.
-Allen