This video shows me going through the steps to replicate this bug.
This is not shown in the video, but during a loaded game, microbe-ambience.ogg repeats over and over and over. Whenever I exit to the Main Menu from a loaded game, one and only one of the main-menu-theme tracks will repeat in a similar way.
At first, it was main-menu-theme-1.ogg, but then somehow I managed to get main-menu-theme-2.ogg to repeat instead, and now main-menu-theme-1.ogg plays normally. I haven't figured out how to reverse it again.
Whenever the music repeaty-thing happens, the console spams "[Error] OpenAL Error: Invalid Value."
I overwrote my old save, and the same thing happened, but with different audio files each time. This time it was one of the microbe music tracks that was repeating, along with the ambiance. All other microbe musics played normally.
So apparently it's got something to do with loading games?