V480 PROM update causes odd reboots

I have a V480 running Solaris 8 02/02 that I recently updated with the most currnet PROM OBP 4.18.2. Now the server is rebooting itself every night between 11pm and 1am. Sometimes it reboots once, sometimes twice or 3 times. There are no crons running that could cause this so I'm not sure what the problem is. There is nothing in the logs to indicate a hardware problem, nothing in the logs at all actually. It's very strange. Would an upgrade to Solaris 9 help? Or is it possible to downgrade the OPB back to what it was running before (OBP 4.7.x)? Any advice would be greatly appreciated.

[600 byte] By [manheim] at [2007-11-26 6:04:50]