Comment 16 for bug 214370

I WORKED OUT THE PROBLEM

It's all about the PulseAudio, the new sound server in 8.04 Hardy,. Instead of that every application has its way to access the sound card, PulseAudio becomes a common (gate) to access ur sound card. The problem is that not all applications can deal with the new sound server. But it's getting better.

Apparently System Sounds have also a problem dealing with PulseAudio to get over it i installed "PulseAudio ESD compatibility layer" u can install it by :

[Code] sudo apt-get install pulseaudio-esound-compat[/Code]

One last thing:
-Make sure that PulseAudio is configured the primary sound device (System>>Preferences>>Sound) and in the Device tab select PulseAudio Sound Server, sometimes it will require a system restart to work properly,
-Make sure that Software Sound Mixing is enabled from the Sounds tab in Sound Preferences check "Enable Software Sounds Mixing ESD"

I posted the same issue here and i figured out the solution later http://ubuntuforums.org/showthread.php?t=789280
Also be sure that u will face other problems with PulseAudio this thread is really helpful http://ubuntuforums.org/showthread.php?p=4725430

It's totally true as David Clayton said above installing esound only in Gusty 7.10 fixes the issue BUT in Hardy 8.04 it freezes my whole system directly on start up.
And about the logout sound i do agree on the fast PulseAudio shutdown theory but i'm optimistic concerning PulseAudio in general. No one could disagree that's better than the previous sound mess in former Ubuntus.