I dont' remember where I heard it from (could be B.S.), but someone once told me about a Jeep Cherokee they purchased that had something that kept rattling around underneath. They searched for years trying to figure out what it was. I don't remember how they found it, but someone at the factory had taken a golf-ball, and placed it in one of the frame rails during manufacturing. On the golf-ball, it was written "Hard to find, eh?".

oh:
Like I said, this could be B.S., but it makes for a nice laugh.