MacBook Air is reducing Volume to very low on bluetooth and Mirroring to Apple TV

The volume starts off for 1 second normal, then it cuts back. I am a teacher and yes my Apple TV to connect to the school tv to use PPT and Show Youtube. I have a brand new MacBook Air. The volume on the School TV is so low that it is unusable. I thought it was the TV, so I brought in my JBL Charge 5... plenty loud on my iPhone, but the problem persists. Not only that it also happens with Apple Music played from my laptop. It starts loud then scales back so that max volume is needed on the laptop, and bluetooth speaker to hear anything at all. I have disconnected and reconnected everything. nothing has helped. all of the volume sliders on the apps and system are maxed out as well as the speaker. please help.