So with my relatively new 7d I had a few random dark spots show up in a couple pictures. Was shooting at someabandonedwar base (not saying that was the cause [:P]). It was hot out (actually it was ~108) , but shouldn't a 7d do ok in the heat?

Only shot ~50 photos that day, only 3-4 photos showed with the dark spot..





B&W helps show the spot a little



black levels raised even further in this pic to bring out spot





Thankfully I didn't care about this shot much... just don't want this to occur again


Any ideas appreciated. (and yes optics were clean, shot at 24mm with 24-70 2.8L)