It's a tray-loading iMac.

I haven't experienced the glass sound myself. My sister claims it only happened once :-/ I've only seen it shut off twice myself. Once after starting it up it shut off right after it showed the happy mac. The second time was when she turned it on and it shut off in the middle of booting the OS. It's just odd whenever it decides to have fits. After those two, it booted normally and ran for a couple hours before we turned it off.