Why does my MacBook sometimes ring the startup chime four more times after the initial chime?

Does it happen in quick succession to where you could say the the unit chimes 5 times at start up? Or does the system reboot between each chime?

If they happen in quick success I would suspect a RAM Module issue. If it is so that the system reboots each time I would lean more towards an issue with the MLB's boot ROM. Late 2006 MBP parts are getting scarce since a Apple computer can only be serviced for 5 years from DOP. Hopefully that will give you a bit of information.

Another (distant) possibility is that the OS is corrupted after trying to do a software update. That one is a bit tricker to find but best tip is to run a complete backup of the unit, re-install the OS from the DVDs that shipped with the unit and the reapply all available updates (making sure the unit is attached to power the entire time).