Sound broken in flatpak

Hello,

Sound is broken in the flatpak release of ~~2.0.0~~ 2.8.0 (it may well be for others, too, but I haven't tested them and have since decided to continue avoiding flatpak).

I first noticed this when playing I Have No Mouth, and I Must Scream, where the music appears to work fine, but aside from the opening monologue, no voices are ever played.

After installing the .deb for ~~2.0.0~~ 2.8.0, voices, sound effects, and music all work as expected, not only for this game, but also for other titles I have since gone back and checked. I had previously played the entirety of The Secret of Monkey Island and part of Monkey Island 2 on the flatpak version, without realising that both of those games actually have sound effects and not just music, which the .deb reproduces without issue.

Needless to say, I have moved my game playing to the .deb release, but as a courtesy to the community I have decided to open an issue here. I'm not sure what could be wrong—I have verified that my settings were identical between versions—but I also have a hard time believing that a release could happen with such high-profile games being fundamentally broken without it somehow having been of my doing.