Best answer by Ryan S
I'd like to suggest again that you take the time to give us a call so we can look into this closer.
In the meantime, would you mind submitting a diagnostic from your Sonos system and replying back with your confirmation number while you're getting these sync issues? I'll send them up to the team to look into just in case something is being flagged there. We've seen similar issues with certain TVs not handling Dolby Digital audio quickly enough and sending it slightly delayed. If this is the case, setting to Stereo or PCM would resolve the issue, as would using an HDMI switch instead of the TV. However, this would make the CEC commands not work from Beam.
Please note what TV model you're using here, and also, how the Beam is connected to it.