I bought the tablet and use it for about 5 days. Yesterday the audio stopped working. It was weird that only the alarm and email notification sound worked and the media sounds didn't play. Try changing volumes at max volume and doing Factory reset, but no avail. Plugging in headphones actually produced sound. I haven't rooted the device.
Today my Nexus 7 starts working spontaneously. It plays for 5 hours, and goes out again shortly, but now the sound is completely there. Maybe it's a software issue.