Comment 2 for bug 1734100

I don't think the problem is with indicator-sound/-gtk2.

indicator-sound Recommends one of the following ( | = or)
unity-control-center | gnome-control-center | ubuntu-system-settings | pavucontrol | mate-media

It seems a sensible thing to do would be to make lubuntu-default-settings pull in pavucontrol to satisfy the dependency, so that unity-control-center and its associated packages don't get installed.