What devices are cabled to the TV besides the FireTV Cube? If there are others, try switching off CEC on those devices too.. also ensure you have "TV Autoplay” enabled in the Beam’s room settings in ’Settings/System’ in the Sonos App - if it is ‘ON’ then try toggling the switch ‘OFF’ and ‘ON’ again. See if that sorts it.

I have 3 devices:

Fire TV Cube

Sonos Beam

Virgin 360 TV Box

It is a Panasonic TV and I have had issues with CEC settings before but cannot find a means to adjust it on the TV which is a pain.

I assume you cannot switch off CEC on the 360 box, at least it wasn’t possible to do that on their older V6 TiVo box, but maybe simply try it on a different HDMI input and see if that assists.. you could add a CEC-less adapter too, but I would do that only as a last resort. 

Maybe check the Panasonic site for any TV firmware updates.

Also did you check/toggle the TV Autoplay feature too?

Panasonic are hopeless when it comes to Technical Support.

They are very insular and I have never closed out a question of a technical nature with them.

I did toggle the TV Autoplay feature, and you are right about the TV 360 box there isn’t a way to switch of CEC.

I have things working at the moment and hopefully by trawling the internet I may find a solution.

@Laguna8, 

As you are unable to switch off CEC on the VM 360 box, there are these adapters that can be inserted between the device and TV to stop any problems and block CEC… so that’s an option if you perhaps find the 360 is the ‘culprit’ and attempting to steal the focus away from the Arc…

https://www.amazon.co.uk/LINDY-HDMI-Less-Adapter-Female-Black/dp/B00DL48KVI

Thanks Ken

Hi Ken

I bought the CEC less adapter, plugged it into the FireTV cube port and so far no sound issues at all.

Keeping my fingers crossed that this is the solution 

Thanks for posting back - hope it works for you.