Thanks for the response. What I see above my head appears to be a speaker, there is an identical one above the passenger seat. My voice command works ok from the drivers seat, but cannot hear commands from the passenger side. Don't have the problem in my CTS.
To my knowledge it is not a speaker, they were also in the headliner in my 2014 CTS and my wife's Acadia Denali also has them in the same area. I'm pretty sure they are too small to be a speaker., they just have a speaker-like grill covering them. You can always cover it up and see if the voice command can still hear you.