Pretty straight-forward setup: AppleTV 4K connected to HDMI 2 on my Sony TV. HDMI-ARC out of the Sony into my Sonos Beam. This was working perfectly.
Now, a mystery: I moved into a new home, hooked everything up in the same way as before (I think!) and now I can't get sound from the AppleTV to the Beam. My Sony TV is set to 'external speakers' (it did this automatically when I connected the HDMI cable from the ARC port to the Sonos. The Sonos itself is working otherwise (i.e. I can play music through it either via the Sonos app or by AirPlay).
Suggestions? I'm going mad!