hello,

how to modify (or get rid of) the sound (music) that is played when the computer starts ? (with ubuntu).

Thanks.

On Ubuntu 9.10 go to: system > preferences > gnome login sound, and uncheck the box next to that.
There may be other options under: system > preferences > sound, that you can modify. However, I have removed the resource hogging Pulse Audio, so I can not check that, since the sound preferences app needs pulse audio to work.
Unchecking the gdm login sound should do it though if I remember correctly.

Big fat edit: The correct path to uncheck the gnome login sound should be:
I meant to say, go to: system > preferences > startup applications. Then uncheck the box next to gnome login sound. This edit is to correct what I first posted above.

I also find the "Ubuntu drums" to be rather annoying when I login.

Hello,
I have ubuntu 910 but I don't have a gnome login sound in preferences.

Where can I find this then ?

Go to System/Preferences/Sound, from the drop down menu for 'Sound Theme', select "No sounds" to eliminate the default login sound.
The default login theme will be found at /usr/share/sounds/ubuntu/stereo. You can create your own, or possibly substitute your own .ogg sound file in a theme. Or you can download and install other themes at http://ubuntu-art.org.

I'm very sorry, but I made a mistake in my last post.
I meant to say, go to: system > preferences > startup applications. Then uncheck the box next to gnome login sound. The sound should be gone the next time you login to Ubuntu.
Sorry for the inconvenience. Please post back if this helps, or if you need more help.

What Brains posted above should be helpful to you also. You can change many sounds from: system > preferences > sound. I no longer have this, since I removed pulse audio.

I have edited my last post to correct this for the benefit of others who may look at this thread.