Visible crew/equipment: During the wide shots of the freight train, special brackets are prominently visible underneath the door of the box car in which Ice Cube and the kids were riding. None of the otherwise identical boxcars have these brackets, which were probably used to support a removable camera during the close-up action scenes.
Visible crew/equipment: When Nick first pulls up outside his store in the Navigator, Marty comes out and starts admiring it and you can see a camera man reflected in the window next to the door.
Chosen answer: It's called the "Hamster Dance Song" by Hampton the Hamster.