iPad (1st Gen.) Using WiFi in Sleep

I have an original iPad running iOS 5.1. Just recently, the iPad has continued to use wifi while in sleep mode. It is transmitting data over wifi enough to slow all of my other devices by at least 1 mbps (on iPhone 4 speed test shows 2.5mbps over wifi with the iPad wifi disabled and 1.5mbps when the iPad wifi is enabled). I know it is the iPad because once the iPad wifi has been disabled or the iPad has been turned off completely my data transfer rates over wifi shoot back up and all of the data lights on the router stop indicating that there is data being transmitted. I just noticed this issue yesterday. I have tried force closing all apps from the multitasking tray to ensure nothing was running in the background, hard restarting (holding lock and home buttons) the iPad, connecting to different wifi networks (dual band 2.4 & 2.5 ghz signals), resetting the network settings on the iPad, and resetting the router and modem. None have worked. I plan on restoring the iPad completely as a new device later this evening, but wanted to see if anyone else was having the issue as well. Is anyone else experiencing this?