I could almost guarantee that you broke it, or at least put enough stress on it to crack it, when you where wheeling and then it just took a while for the u-joint to finally go. either that or a c-clip fell out and the cap slowly worked its way out.
btw mike, what you broke is called the muffler bearing. you should probably check out your blinker fluid too. and you def need to tell the dealership to rotate your lug nuts and change the air in your tires.