What is "Power Nap" you might ask? Something that is absolutely useless and unnecessary, yet Apple decided it was wise to include it in OSX 10.8. Perhaps it makes sense on iMacs or other desktop units, but not on laptops. In a nutshell, "Power Nap" allows your Mac to do things while it is technically asleep like fetch emails, update calendar items and such. Basically, it negates the whole purpose behind sleep mode. If you want the whole writeup on "Power Nap" check out the Apple KB Article on it here: http://support.apple.com/kb/ht5394.
Anyway, to get rid of the problem, just disable "Power Nap".
- Open System Preferences (from the Apple menu on the top left of your Mac)
- Click 'Energy Saver' (the CFL Lightbulb Icon usually on the second row, third one from the left)
- Click the 'Power Adapter' tab (as opposed to the Battery tab that opens by default)
- Uncheck the 'Enable Power Nap while plugged into a power adapter' (see image below)
- Close 'System Preferences' (and test to make sure this worked for you!)
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