Ubuntu 12.04 locks up when it tries to play a sound

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http://askubuntu.com – I have a new installation of 12.04 on a new desktop PC. According to Update Manager, it's all up-to-date. Very reliably, the desktop will lockup whenever it tries to play a sound effect. I can open up Terminal, then press Tab once (which usually causes a system beep), and the desktop is now locked up. The mouse cursor can still move, but mouse + keyboard has no effect and the display is frozen. From there I can Ctrl+Alt+F1 to get to a command line, then stop and start 'lightdm' to get a new running desktop. The bug is repeatable from there. A related issue, if I try going to System Settings (HowTos)