well, the rumbling of the aircraft as it flies overhead, perhaps 20-50% of that caused by a large lorry passing 10ft away in the street may contribute to loosening tiles ?
I suggest umbrellas or bike helmets at all times, or make roofs out of straw like they used to do.
(Is it me, or did the news girl seem to have one of them Jamaican accents? I was all expecting Ali G to bust out of the woodwork with a gotcha!)