Background music volume goes up when active HEX speaking

**Describe the bug**
I usually have background music, but every time I activate HEX, the background music volume increases. However, after I deactivate HEX for a few seconds, the volume returns to normal. It's very annoying.

The issue does not name a file, test, or entry point. Start by locating the macOS audio-handling code in this legacy Swift app and reproduce activation while background music is playing; done means HEX speech no longer causes the music volume to increase and the existing volume behavior remains stable after deactivation.

Written by the indexing model from the issue text.