There are plenty of forum posts and conflicting advice out there, but here is what works:
Commands to type:
sudo mv system-ready.ogg system-ready.ogg.disabled
Shown as a screenshot here:
Now restart your computer, and check the login screen, no longer gives a drum roll.
Before the change - how did everything look (default):
Recap - describing what I did:
The drum roll when the greeter screen (lightdm) is first displayed, is the system file
system-ready.oggis a symbolic link to the actual sound file
By moving system-ready.ogg to new name system-ready.ogg.disabled,
the Ubuntu system is unable to find what it has looked for, and you get what you want - silence!
No more drum roll every time the Ubuntu login screen is displayed.
Previous versions of Ubuntu and Gnome:Ubuntu 11 and earlier did have a more Graphical and user friendly way of disabling the login drum roll.
There are plenty of forum posts about that.
To clarify: Advice that works for 12.04 lts will be different to advice that works for Ubuntu 11 or Ubuntu 10