I had this similar issue a few months ago but in a 2019. I usually have the sound between 8-12 and you can hear the music clearly, even with the windows down on the freeway. One day, and it’s only happened one time, I could barely hear music even on 20. Thought either the sub or a speaker went out but I decided to switch it over to the radio, and the sound was fine. Then I started random directions on my phone via CarPlay to hear the loudness of the prompts and it was fine as well. Went back to Bluetooth and the sound was back.