Interesting. As you’ve surmised, if it is connected by ARC or eARC, it shouldn’t be doing that. I’d likely check several things. First, make sure the HDMI cable that came with the Beam is inserted all the way at both ends. On the TV side, it must be in the HDMI port labeled ARC or eARC.
Next, I’d take a look at the TV’s settings. Make sure CEC (or whatever your TV manufacturer calls it) is turned on. Since you haven’t mentioned which TV it is, I’m taking the assumption that it does have ARC, which is part of the CEC.
Next, I’d check the TV’s settings for updates. It wouldn’t hurt anything to unplug both the TV and the Sonos from power, for at least two minutes. This should reset both of them, especially if something odd has occurred with the power.
However, if none of this makes a difference, I’d call Sonos Support to discuss it.
When you speak directly to the Support staff, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.
