Lately my iMac G5 (20" w/iSight) was been acting a bit weird. Things are showing up on the display that shouldn't be there. For example, if I'm using Safari and then quit, if I use Expose after, I can still see a very faint image of the Safari window. Also, when I'm playing games, there's a faint image of the menubar. Eventually it fades away, but it's annoying while it's there. Is this normal? If not, what could be causing this?