im having this problem along with the 3rd gen that i hang out with. i havent started to work on it and figure it out yet but if i figure it out ill report back.
EDIT: ive done a bit more research on this and its sounding like its most likely the starter.check all the connections and grounds for it and if not then you can try to replace the brushes on the starter if you go to napa and order them. ill be doing it this weekend so ill let you know.
http://www.napaonline.com/MasterPage...=Starter+Brush