Adding audio only from a clip, but it's silent.

iMovie is driving me nuts. I'm editing the third episode of a web series, and something I did often in the other two episodes suddenly doesn't work. When I detach some audio or use cutaway with audio only, the audio is clearly there, as a purple clip, but it is silent. I found one other question from two years ago that seemed to be the same problem, but it was never solved.