Random Volume Indicator popping up on left side

[mberneis]

I noticed lately that a volume indicator is popping up on the left side of the screen. - It does not seem to affect navigation or music volume but can be clicked on and would turn 'off or on' (crossed out speaker)
Another strange thing is that the icon is black, not gray as the other UI elements around.
It took me several days until I could take a picture of the icon as it disappeared as soon as I pulled out my phone...

I noticed the icon coming up when I am waiting at a stoplight and the car display is centered from the top instead of perspective.

I do not have a passenger warning system installed (as far as I know)

Does anybody know what this is and which volume it controls?

 

[RTPEV]

This is the proximity sensor alarm mute button. When you are stopped at a stoplight, or going through a drive-thru or something like that where you are close to other cars or obstacles, the car will beep if you get too close to them. If you don't want all that beeping, you can hit that speaker icon to mute it.

 

[mberneis]

Thank you - I will pay attention to this the next time - Although when I took the picture I was in the middle lane with no cars around me...

 

[ilyak]

Thank you - I will pay attention to this the next time - Although when I took the picture I was in the middle lane with no cars around me...

You can see just a hint of the proximity alert outline ahead of the car on your screenshot.

 

[SVMike]

This also took me a month or two before I figured out what it was.
This is an example of a cool feature of the nice big screen.
It is probably also a deterrent to non-techies since there are so many things like this you have to discover about the car that aren't in the manual...or if they are it is obscure.