I had that once when my G68J locked up when scrolling through the menu to adjust the lipsync delay. Fried a tweeter instantly (luckily just one). I had to ran to my amps to turn everything off manually.

Ever since I added a G91DH to my system, the system had it quirks. Although lately I have less problems, occassionaly one of the speaker will 'spike' briefly when playing a movie. Most likely caused by the source material (I play mostly off-air HD material) so that can have it problems, but still you expect the processor to filter it.

G68J, HD621, ...