This starting happening about a 4 days ago. My headphone jack fails intermittently. I have speakers hooked up to it and sometimes sound will not play through the speakers. Even if I disconnect the speakers and plug in headphone sound does still not play through the headphones. I have even tried restarting and that does not work. In my system preferences (In Sound Panel) it shows that something is connected to the headphone jack. I have already had the entire logic board replaced once (under warranty) and that seemed to fix the problem for a couple months. If I wait about a day or less magically the speakers start working again. This has happend twice. Has anyone else had this problem? I have about 2 weeks left on my warranty. It almost seems like it is a software problem now, but I am not sure.