sonos beam

How do you control vomume? Via Sonos app, tv remote or voice control?

Hi by Apple TV remote if I turn it up it stays on for a few seconds then on the left of the screen numbers appear then count down on there own till volume is off 

Also the beam goes to Green 

​@Logins 

That imo indicates a repeating command reducing Beams vomume until it mutes (green led). 
Please check your AppleTVs remote settings in tvOS settings and also your tvs hdmi cec communication settings. 
You should avoid using remote simultaneously via infrared and hdmi cec. 
I suggest to try via hdmi cec and if that doesn’t work to try infrared. Using AppleTV remote usually you don’t have to run the ir remote pairing via Sonos app as atv remote is recognized automatically. 

https://support.sonos.com/en-us/article/use-an-apple-tv-remote-with-sonos-home-theater-products

How long after you attempt to raise the Volume does the Volume go down? Do you have a similar response when attempting to lower the Volume?

If the Volume reverts to the previous value, I suspect a communication issue between controller and BEAM 2. As you drag the Volume bar, the bar will respond in real time while attempting to send commands to the player. A second or two later the controller will interrogate the player and update the display to show the player’s current Volume. If one or more original Volume commands were missed, the display will report the current Volume — which may not be what you expect. I also suspect that there is a minimum dwell time as you drag the control before anything is transmitted to the player. You can test this postulation by dwelling slightly longer at the new setting before removing your finger.

Are you more successful if you touch the slider track rather than dragging the dot?

You can submit a diagnostic and follow up with Support. Communication issues, if any, will leave tracks in the diagnostics.

Update: Hmm, my typing is a bit slow. What is the current Volume when you attempt the change? What is the desired Volume?

I suppose the ATV remote could have been paired manually within Sonos app and the wrong (reverse) volume button could have been used for pairing. 
If so, try pairing it again or deactivate IR usage for Beam within Sonos app settings and just try hdmi cec control.