I went to the Apple store today and the guy opened the laptop and said that the Airport card was just a tiny bit out of its socket – which he didn’t believe was enough to cause a problem, but I figure that the fact that the problem mostly happened when the laptop was warmed up and moving, makes perfect sense. He also said he put some insulating tape over the card as well so it wouldn’t make contact with the frame.
It’s been several hours and it hasn’t happened since. Woo hoo!