Machine hangs every 30 minutes like clockwork

Question

Within the last couple of weeks, my system has started to hang like clockwork every 30 min.  No idea what caused it and don't remember anything in particular installed or done during that period.  Unfortunately, when it hangs - there is nothing kicked out in Console and there is no recurring "this process was running right before it happened" clue.
Details on system:
Macbook Aluminum (late 2008)
Mac OS X Lion 10.7.4
2 MB ram
30% harddrive space free (approx. 90 GB)
What I've tried:
-repaired permissions
-repaired drive
-cleaned up drive via Cocktail, CCleaner, CleanMyMac and Disk Doctor
-reset PRAM
-reset SMC (which, thankfully, solved an out of control fan problem)
-tried booting in Safe Mode (and it didn't seem to occur)
-reinstalled Mac OS X Lion
The hang is most obvious when watching a tv show or video - but this may simply be because video and audio suddenly stopping is much more evident then at other times.  I believe it has also happened while I'm just working pages.
Any thoughts on how to tackle this next?  The fact that it didn't occure in Safe Mode makes me think that it's a login/startup item issue, but I'm unsure of how to tackle this without breaking something.  Is there any way to see what's going on at a "deeper" level then Console?
Thanks for any help or direction you can offer.  I've spent the last 4 days tackling this and while the computer is running smoother, the "I can set my watch to it" hang ever 30 minutes is annoying.
Thanks!
Daniel

Answer 1

So, I have no idea what it was.  In the end, I decided to just go for a clean install.  I had a time machine backup and then a seperate backup (I'm in the middle of my PhD research, so I was nervous about loosing anything).  But, wiping and reinstalling was easy.  Here's the process I went though, in case anyone else is interested:
1. I made a bootable DVD of Mac OS X Lion last year when I upgraded (you can find directions for making a USB or bootable DVD online).  This isn't necessary if you have a fast internet connection - as the Lion Recovery tool (CMD+R at boot) will redownload Lion from the App Store for you. I'm currently in Africa and due to the speed of our internet, that wasn't an option.
2. I restarted the computer, holding down CMD+R to boot into Lion Recovery.
3. Then used Disk Utility to erase the drive.
4. Then I inserted the bootable DVD and restarted the machine, holding down "C" on boot this time to force a bott from the DVD.
5.  Went through the process of reinstalling (warning, it took a LONG time for it the install utility to come up from the DVD, you just have to be patient).
6. I reinstalled from the DVD which was a quick and painless process - 30-45min.  Set your initial user as Admin, as you'll transfer the Time Machine material to a new user.  (Also, having an admin account keeps one account "uncorrupted" should an app install mess with your normal user account).
7.  After install, I ran all the system updates I could (included a 1.5 GB update for Lion 1.7.4).
8.  After all the updates were run, I then plugged in the Time Machine and ran "Migration Assisstant" from the Utlity folder.  The restore from Time Machine was slick.  It completely brought the user back with our wallpaper, dock settings, apps, etc.
That's it.  Everything seems to be working much better - smoother, quicker - then before.  It's actually incredible what an increase in speed just doing a clean install (I had originally upgraded to Lion from Snow Leopard) has made.  It's like a brand new computer.
I hope this might be helpful for others.