Comment 7 for bug 282383

as best I can tell, this is the responsible package. from the description of the package:
This module enables PulseAudio to publish itself as the default sound server to the X11 root window automatically upon startup. The is also a module to playback a sound file in place of the X11 bell beep.
I hope I should assign it to this package and not pulseaudio. If this package isn't the problem, maybe we can track it down from here.