When opening pavucontrol.glade with Glade 3.22.1, this message was
shown:

    pavucontrol.glade targets Gtk+ 2.16

    But this version of Glade is for GTK+ 3 only.
    Make sure you can run this project with Glade 3.8 with no deprecated
    widgets first.

I think it's best to just drop the gtk2 support.