Mac wakes on scheduled power event that recreates itself every day

At 2:14 every morning, my Mac wakes. Looking at the logs, I see it's a scheduled event, but nothing shows up in System Preferences > Power. When I go to terminal, and run pmset -g sched, I see

Scheduled power events:
[0]  wake at 03/31/13 02:14:00

Only one, for the next event. I can delete it through pmset, and it won't wake that night (morning). The next day, there's a new event. So for instance, after that one went, now I see

Scheduled power events:
 [0]  wake at 04/01/13 02:14:00

I've locked the Power Management preferences, I've even set the com.apple.AutoWake.plist file to remove all write access through chmod, and the next day… a new entry appears.

Taking Lauri's suggestion, I ran opensnoop on the Autowake.plist, and at 2:15, this happened, inserting that power event:

2013 Apr  4 02:15:00     0     20 powerd         4 /Library/Preferences/SystemConfiguration/com.apple.AutoWake.plist 
2013 Apr  4 02:15:00     0     20 powerd         5 /Library/Preferences/SystemConfiguration/com.apple.AutoWake.plist 
2013 Apr  4 02:15:00    89  15241 mdworker       4 /Library/Preferences/SystemConfiguration/com.apple.AutoWake.plist 

I didn't see anything in /Library/LaunchDaemons/ or /Library/LaunchAgents/ that seemed relevant. Execsnoop returned

2013 Apr  4 02:15:00    89  15241  14058 mdworker
2013 Apr  5 02:15:00    89  24165  19851 mdworker

What the heck is going on, and how do I stop this from happening? Or what's the next step to troubleshoot this? Thanks.

Vitals: it's a Mac Mini, 10.8.3, but it's done this for ages (including when migrated from a previous Mac Mini via Time Machine).