Answer to: iPhone 4 head phone jack producing sound only on right headphone?Have you checked your Settings yet? Go to Settings > General > Accessibility > then scroll down to Hearing, under where it has LED Flash, Mono Audio, and then L/R. Make sure its centered. If it isnt, do so. If it is, you have a obvious hardware issue. My settings where panned all the way to the Left. I thought my iPhone was having the same issue until I realized this option somehow got changed. Good luck.