ipad auto tapping, upper left corner.

I recently bought a used iPad Gen3 3G+WiFi with IOS 7.1.2, fully functional from a friend of mine. The device worked perfectly for 3 days, and then it started self tapping in the upper left corner. The device does this sporadically, when i least expect it. I tried restoring the device to factory defaults via iTunes, but it still does this every now and then. The device hasn't been dropped or anything (since its been in my possession), it came with its protective case, no dents on the surface of the screen or the corners whatsoever (none that i can see at least). Is there a way to fix this myself via software or do i have to take the device to the genius bar and have it analyzed? Any help will be most appreciated.