There is a very annoying sound (a drumroll) at the login of Ubuntu 11.04 (I think it applies to earlier version to, although this method of disabling it does not, it should however work on Fedora 15). There is a gui (System/Administration/Login Screen) for making this happen, although it seems rather broken (read about it here). Nowadays dconf (gsettings is the api) is used as backend rather then gconf, although not all applications has adapted this, gdm has.

So what it boils down to is basically “set the right gsettings for the gdm-user (since gdm is started by the user gdm)”. Here’s how,

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# Become root in whatever way you want, <br>
su -

# Start a shell as the gdm-user, 
su - gdm -s /bin/bash

# Start a session-bus,
eval $(dbus-launch --sh-syntax)

# Set the right settings through gsettings, 
gsettings set org.gnome.desktop.sound event-sounds false

# Logout, 
exit

Thanks to Norman Smith that’s mentioning the above solution in this bugzilla.