I have these not sure which besides soundmaxx that would effect sounds.
Skymaxx V3
Soundmaxx(I tried uninstalling it but it changed nothing the sounds were still missing)
XPGF(for goflight modules was already installed when I got the 737 and there was no issues with it)
Gizmo64 (I think thats related to the 737 isnt it?)
BluFX(kinda like MaxxFX and issue was already present when I installed this plugin)
There are a few others that I have no clue what they do, like XPML.
Also I have the JAR A330 it has a ground handling plug in and some kind of 3d sound,not sure how that would effect the 737
I've also tired reinstalling the plane but nothing changed.