Computer wakes up from sleep mode every 30 minutes

The new version of Norton Internet Security installed on my computer on Saturday, August 8. I'm running Windows 7. I like to leave the computer in sleep mode when I'm not using it. Since the update installed, the computer wakes up from sleep mode, on its own, every thirty minutes. It wakes up, works for about two minutes without the monitor coming on, then goes back to sleep. Then, 28 minutes, it wakes up and does the same thing.

I chatted with a Norton tech last night, who adjusted some settings. But I'm having the same problem today. Please advise.