Well, Mountain Dew's a type of soda, right? They came out with a diet version this year, actually. But if that's not it, it used to be a type of moonshine - when I was younger, they even marketed it that way! As for the words, I can't see much of a connection between the two - the first thing that would pop to most people's mind is the soda, that's for sure.
Is that the riddle, or do you just need help on that part?