You need to avoid DTS/Dolby Digital Plus audio codecs as the TV sound out audio source… set the TV audio-out to Dolby Digital 5.1 and do the same for all other connected devices attached to the TV HDMI ports, such as cable TV, Firestick etc.

If you don’t see Dolby Digital 5.1 then look for ‘Auto’ or Dolby Digital instead, or as a last resort choose PCM, but note PCM will only provide stereo output, rather than surround sound.

Assuming the Beam is connected to the HDMI-ARC port of the TV, the Sony version of HDMI-CEC controls, called ‘Bravia Sync’ also needs to be enabled.

Hope that info. gets your TV up and running with your Beam.

Check to see that HDMI-CEC, or whatever Sony calls it, is turned on in the TV’s settings? Make sure the Beam is connected to an HDMI port that is labeled ARC? Make sure any device feeding the TV is locked to Dolby Digital, and not ‘best’, or DTS, or Dolby Atmos?

Edit: Heh, mostly duplicates of what Ken said, I type more slowly. 

One further thing… in the Sonos Controller App, goto "Settings/SystemtBeam Room Name]” and just check that the ‘TV Autoplay’ and ‘Ungroup on Autoplay’ settings are both set to ‘ON’. They are normally set to ‘ON’ by default, but it’s sometimes just worth double-checking those settings. 

I had the same problem with AG8 and Beam. It seems that Sony defaults audio out to the headphones. Check this on the TV settings menu: Settings > Sound > Headphones/Audio out > Audio out (variable). Then, if you have a green light on the Beam that means it's muted and just bounce the volume up a few times. Worked for me.