PulseAudio, previously known as Polypaudio, is a sound server for POSIX and WIN32 systems. It is a drop in replacement for the ESD sound server with much better latency, mixing/re-sampling quality and overall architecture.
This module enables PulseAudio to publish itself as the default sound server to the X11 root window automatically upon startup. There is also a module to playback a sound file in place of the X11 bell beep.
The modules are called module-x11-publish and module-x11-bell.