OpenMoko 2007.2 makes a very loud startup sound. To mute it, do the following:
In /etc/pulse/session, replace:
load-sample startup /usr/share/openmoko/sounds/startup_openmoko.wav
with:
load-sample startup /usr/share/openmoko/sounds/touchscreen_click.wav
(or any other subdued wav file you wish to upload onto the device).
Update: The OpenMoko team has sensibly replaced the load startup sound with a much more unintrusive sound.