Mine started doing this after being in my pocket while I was in the rain. I tried the rice thing for a day or two and it didn't work. The problem actually got worse over time and it became really difficult to use the phone. Anyway I took the phone apart to look for signs of damage. There was a small amount of rust on one of the screws near the power button but nothing else was visibly wrong. I did notice that even though the phone was powered off the logic board was hot to the touch in the same area. I then unplugged the battery from the logic board. Then proceeded to tear the phone down. I removed the logic board and then the power button frame. Didn't see anything wrong so I reassembled the phone after wiping everything clean with a q-tip. After reassembly the problem was gone. Don't know if you need to take it as far as I did since I didn't find a smoking gun. I'd start with disconnecting the battery from the logic board for a little while and see if it takes care of the problem.