Suddenly my iPhone 4 alternates between Wifi and 3G. When at home, it sticks with wifi for maybe 8-10 seconds, then goes to 3G for 1-2 seconds, then back to wifi to repeat this cycle. It's never done this before. I'm using 4.3.3. I haven't tested it with another wifi network, but no changes have been made to the router and all other devices work as usual with the router. Thoughts?