Two days ago, out of the blue, my iPhone 4 stopped reproducing any sounds over built in speakers, except the ringtone and alarm and the volume bar is missing in the music and video apps. If I plug in my headphones everything is back to normal, sound goes out to the headphones and the volume bar reappears, when I plug them out volume bar disappears again. As I said ringing, alarm and speakerphone are all working, I have tried cleaning the dock connector and the headphones connector and got no result. Any ideas? I am running iOS 5.1.1.