What sound? When connected or when tv is turned on? Have you got “tv auto-play” enabled? 

When TV IS ON. What is TV auto play

Do you mean when the tv is turned on - ie powered on? If so look at Settings/System/room-name and scroll down to tv Autoplay and move the slider to the left. 
 

TV Autoplay means “when the tv is turned on, switch from whatever was streaming and play sound from the tv source”.
 

If it’s something else, you need to give us just a little bit more information or we could be guessing for quite a while. 

This started happening the las couple of days? On a Samsung TV? Maybe check this thread: 

Hi @lizziefaulkes 

Welcome to the Sonos Community!

It may also help to simply unplug the TV from power for a couple of minutes.

If you do have a Samsung TV, however, the issue may be due to a recent TV software update - I recommend contacting Samsung in this case.

I hope this helps.

This is now happening to Samsung owners too and it doesn’t seem to be a LG specific problem as Sonos has stated. It is getting worse now. The audio cuts completely and only an shutdown or changing the audio to internal speakers and back to eArc fixes it. Super annoying. Happens on ATV and internal apps. 

Please investigate further Sonos!

Might be Atmos related.