After starting the box up and placing it in drive, As I start to drive away, after about 20 feet or so, I hear a thunk and some kind of electric motor for about a second.
The sound is normal and I'm not concerned, just curious.
It sounds like something to do with the tranny, but I don't know what.
Anybody know what this noise is?

I read about it in the manual when I bought the car and read about it again last night just to make sure. What you are hearing is the VSC and Anti-lock brakes doing what the book calls a "self-check" to ensure all is well with the system. So "yes" it does sound strange and like something hit the inside of the wheel well or that the transmission is goofing up but........

"no worries"!

It is just our box taking care of us and making sure our trip down the road is protected.