Stop sound from normalizing on Feedback layer?

In my course, I am placing a music track on a Feedback layer. I'm doing this in order to create a default "trigger music" layer that can be applied to any number of slides without uploading the same music track to multiple slides, and to be able to control when that music comes in across different slides.

I have edited the original track to be very low volume, to function as a background undercurrent. However, every time this track plays, it is playing at original (full) volume. I've edited this track in the Storyline editor. I've also adjusted the volume of this track in Audacity and then saved as both MP3 and WAV.

When I preview the audio tracks on their own, they play at the desired low volume. However, when they play in the course, they play at a full volume (much louder than the saved volume of the MP3).

I've experimented with placing these files on a normal slide layer, and the volume is still much higher than the MP3.

My working theory here is that Layers are automatically normalizing volume. Is there a way to stop it from doing that?