This issue has really been getting on my nerves. I never ever had this problem on my 3rd gen iPad until the iOS6 update. From the beginning I was having issues, but I didn't find much about it when I first experienced it in September, only 1 or 2 articles. Sound would randomly disappear from everything except playback adjusting volume in sound settings or with headphones in. Also, the multitasking bar volume slider would dissapeared, along with the volume level indicator when I pushed the buttons on the side. At first I thought it was an issue with the dock connector, thinking the iPad was docked when it wasn't. I started cleaning out the port with a toothpick or plugging in the connector and jiggling it whenever the sound went away, but eventually that stopped working. The sound issues would then stay for longer than they used to in their own, sometimes over 24 hours.
After a week or so the problem randomly stopped coming up, and I thought it had fixed itself. But it began coming back again after a while, before vanishing mysteriously again. It stopped and started coming some more after that. At one point I even wiped and restored the iPad (major pain in the @$$ that was) and even then it contined returning. By the end of October, it had got to the point where now sound didn't randomly go away anymore, but whenever I turned the iPad on after it had been turned off the sound disappeared almost right away (when I would type the password, the first 2 clicks had time to sound before the volume decided to leave). It would usually come back in an hour or 2, when I plugged it in to charge and I could here the sound that it makes.
Eventually I learned to deal with using headphones. I thought that the issue would be fixed when the 6.0.1 update came out, and it looked like it had been. But today... I turned on the iPad and sound stopped working again! I'm starting to worry that all of us will be stuck with this for a while.
I have a theory about what causes it, but I could just be speaking gibberish, it's only a guess. iOS6 must be having some bizarre issues interfacing with the 30 pin connector. It randomly thinks its coked when it isn't and then turns the sound off. I'm guessing this because I haven't got this issue on my iPhone 5 yet, and I would be very angry if I did. But has anyone he'd this problem on a device with a lightning port (iPhone 5, iPod touch 5g, iPad 4 and iPad mini)? That would disprove my theory. But either way, it looks like Apple is having major quality control issues with their software, from this sound thing to their maps of epic fail. Their hardware is disappointing too, my month old iPhone is scuffed to **** and shipped with a defective power brick. Apple, you really are screwing up big time.