Possible reason of CPU spike on specific time frame?

Hey guys,

I noticed that we're hitting 75% of CPU usage at around 4:00PM every day. I checked around the settings and I can't find any setting that is supposed to run at 4:00pm everyday. It was kinda disturbing because we we can't access the PGP server for quite some time until we we forced to ssh and restart the services. Our backups are scheduled at 11:00pm every other day so I'm not sure what I'm missing. We're using Server Key Mode as recommended by Symantec on our specific scenario with key renewal every 2 months. So I dont think that's the issue either. Anything else that you guys might now?

Thank you,