Hi, I'm having an intermittent issue when playing music on my 4S. Most of the time it's flawless but occasionally I'll hear a popping sound for 2-3 seconds. It may then work normally for another hour or so, then give me a few seconds of popping again. I read that OS 5.1 was supposed to resolve some sound issues, but that hasn't fixed it. I've tried different headphones and have also done a restore. I *think* the issue is most likely to occur when the phone is sending/receiving 3G (WCDMA 850 MHz) data, but I'm not certain whether that's the issue or not. Has anyone else run into this?