Sprint's 4.4.2 update included a connections optimizer app which "helpfully" turns on Wi-Fi periodically to find an available network to decrease your data usage. I happened to find it (though I cannot now) to turn it off, as I didn't want it to burn up any battery trying to connect to any network it might find.
UPDATE: I found it, thanks to the following link. It's in Settings > Mobile data > Automatic Connections
This link provides some good pro/con info:
http://www.pocketables.com/2013/02/s...nd-or-foe.html