Audio track greyed out, won't play - related to compound clips?

I'm editing together a virtual choir with 25 video clips on the screen at once all synced to a separate audio track. I've been working in compound clips to get the video clips in the grid that I need, but when I came back to looking at the program as a whole, the audio track is now greyed out and won't play. I can still see the sound waves so I know the sound is there and it's not muted.

I've checked the index roles and dialogue is checked. Any ideas? I'm new to working with compound clips, so I'm wondering if I somehow did something wacky while I was in there...