I would first just try powering off (not standby) all your HT devices for 3 minutes, or so ...and maybe check/re-seat the HDMI cables. It’s best to use the HDMI cable (with heac support) that came with your Arc device, but perhaps don’t hesitate to also try another HDMI cable. 

Ensure that the Sonos Arc is connected to the TV’s Arc/eARC port with CEC enabled and try that port with eARC either switched ‘on’ or ‘off’ to see if that makes any difference. Also check the TV is using its latest software/firmware update from the manufacturers website.

I would leave any other peripherals currently attached to the other TV HDMI ports disconnected at this stage to see what can first be achieved without those interfering in the setup and add them back later when you (hopefully) have things working correctly.

Also see too what volume levels you can get when playing music to the Arc through the Sonos App.

Note you will not be able to turn up the TV volume over HDMI-CEC using the TV remote, whilst the TV is powered off/in-standby.

If the TV remote has been setup for use with the Arc’s infrared receiver, also note that when audio is not playing to the device you cannot raise its volume level, you can only reduce it, this is by-design to prevent anyone accidentally raising the volume high (by sitting on the TV remote for example) and then suddenly having the audio blast out when playing. So maybe ensure something is playing and TV is ‘on’ when adjusting the volume using the TV remote during any testing.

Hi @Jengalee84 

Welcome to the Sonos Community!

If you haven’t already, I recommend you get in touch with our technical support team who will go through some troubleshooting steps with you, perhaps leading to a replacement cable or unit.

I hope this helps.

Thanks for the help guys, I powered down the system and let it reset, powered it back on the arc did an update, the problem has now gone!

Thanks again