I am sorry to hear you are experiencing this issue. Does the audio dropout happen on all sources?
I just bought a UN55F6800AFXZC to replace my UN46F6500. The TV is connected to a 2.1 Bose home theater system through the optical out. The sound cuts out every few minutes for a few seconds.
There was no audio problem with the exact same setup and my previous TV.
I upgraded the firmware but it didn't solve the issue.
Any feedback is appreciated.