emacs 23.3.1 freezes on Ubuntu 12.04.3

I have a ubuntu 12.04.3 system recently upgraded from 10.04 LTS. After the upgrade, the X version of emacs freezes a few minutes after startup, while I am working. The exact failure is that the emacs window goes dark, like perhaps it's preparing to minimize, and emacs immediately begins using 100% of CPU. I cannot get it back and either have to kill -9 the process or simply close the window using the X button in the upper left. I am using the default window manager with the default theme. I have had reasonable success reproducing the bug by marking text using C-spc and then copying it with Alt-w. This doesn't always work, but it's the one single thing that I know can trigger the freeze (and of course, I use that key combo all the time). I've tried doing the above with the mouse in different positions, thinking that perhaps the window manager was misinterpreting key-strokes intended for emacs as window manager commands, but I don't get consistent behavior. Any advice on how I might to about investigating this problem would be appreciated. Please... I don't wanna learn VI!