My TIVO box can start to drop the audio for a second or so every 3 minutes. I can fix this by putting it into standby and then out again, this will stay OK usually until I put the TV into standby / off, then it can restart again once the TV is back on.
I've been through every audio setting on the TIVO, nothing seems to fix this.
I did factory reset the TIVO and then had a full week running without this problem, it has now just started again.
The TV doesn't do this with my PS3 or Kodi, just the TIVO.
the problem has always been present on since I have switched audio to optical. As I said though it is intermittent though if the TIVO is restarted it will pretty much remain ok for the duration of that session.