Sound definitely works on the GazP3.
Make sure you have installed *and* ran your System76 Driver...
To install the System76 Driver, navigate to http://planet76.com/repositories and download the latest .deb package. It will be the one closest to the bottom of the page. Save the package to your Desktop and, when it has finished downloading, double-click it to launch the Gdebi installer. Then, click the install button.
Once the package has installed, you can open the System76 driver by going to System > Administration > System76 Driver. To install the drivers for your machine, Click the "Install" tab and the "Install" button. If you are restoring your machine to factory settings, Click the "Restore" tab and the "Restore" button.
When the driver has finished running, reboot your computer.
And then, make sure all of your audio channels are opened and set...
First, run your System76 Driver (System > Administration > System76 Driver > Install Tab > Install Button) and reboot your computer.
Second, double-click on the speaker icon in the upper right corner of your screen. In the resulting Sound Control Panel, go to Edit > Preferences. (If you are using Ubuntu 8.10, you will have to click the Preferences button.) Make sure all available checkboxes have been selected. This will make more sliders available on the sound control panel. On the sound control panel, make sure that PCM, Master and Front (or whatever combination of these you have) are not turned down too low or muted.
Third, go to System > Preferences > Sound. Make sure all drop-down selectors are set to ALSA. (If you are using Ubuntu 8.10, make sure all of them are set to Pulse Audio instead.) Click the first Test button to see if you now have sound.
Pay attention to the Pulseaudio part.