Comment 1 for bug 718805

Right, I have investigated this bug further.

Because Natty does not have gtk+3.0 as a default installation, packages libgtk3.0-0 and libgtk3.0-common are not installed.
This creates a problem concerning libcanberra.

To be able to play system-ready (drums) and login sounds, an executable file "canberra-gtk-play" must be installed
(into the folder /usr/bin).
The latest libcanberra_0.26-1ubuntu9 installs it only with the package libcanberra-gtk3-0.
However, libcanberra-gtk3-0 depends on libgtk3.0-0.

So, without libcanberra-gtk3-0, it would be possible to install the executable "canberra-gtk-play" with the package libcanberra-gtk-0.
This is how it was done in the version libcanberra_0.25-0ubuntu1. In the later version the file was removed.

OK, to test this (this is also a workaround),
first check, that libcanberra-gtk3-0 is not installed.
Then copy (backup) the file "canberra-gtk-play" from the package libcanberra_0.25-0ubuntu1.
Then, install the latest version libcanberra_0.26-1ubuntu9 (this way "canberra-gtk-play" is not in your system).
Lastly copy paste the file "canberra-gtk-play" into the original folder /usr/bin.

Now the system-ready and login sounds are back.

Note that this bug does not influence event sounds (libcanberra-gtk-module).