Inaudible Mode
playback at the lowest level of volume to diffuse the bio active sonic vibrations without hearing the music
This seems to be a thing with German cars, of which I have two. If you switch off the car audio, it will come back on next time you start the car. But it does so at an almost inaudible volume, so you spend the next hour driving around while searching for the source of the annoying whispering sound, and maybe concluding that you're hearing voices in your head.
It's almost as bad if you turn the car off while the audio is playing. When you restart it comes on at about half the volume you left it at, so you spend the first five minutes fiddling with the controls to get it back the way you like it. I remember old-fashioned, pre-digital audio where you could set the volume once and it would be right for the life of the car.
And why is Bluetooth streamed audio always at a small fraction of the volume of other audio sources, including BT phone calls? It's just a digital transmission, so it has no intrinsic volume. Somebody just decided to play BT music in inaudible mode.