Now thinking about it, I actually think the magnet is built in to the bottom of the differential because that's the only place the piece magnatized to.

I took a picture of what I'm talking about that I think is the magnet...
http://i887.photobucket.com/albums/a...-04-31_413.jpg

It sits at the bottom and that's where the metal piece was. Like I said though, everything looks good and is still moving freely, so as far as I'm concerned, it's ok. I'm gonna go up to the service dept at a car dealership tomorrow and get one of their techs to look at it and see if they know what it is.