Whats amazing is the OP didnt provide enough info for us to know much of anything here…and the info provided may be inaccurate. IF it is a lien, or if it was a line of credit is what most imortant. Best suggestion I saw is to call the bank involved and ask what the payoff is…but the reason that isn’t happening is I believe the OP wants the 2k for his pocket now and to just keep making monthly payments… thus flush with cash for other shit now. So the question you want to know is… will the bank involved know u sold it. The answer is, probably not, from the info you have provided.
You have apples and he has oranges. You just suggested that he commit a crime. 
He suggested the bank indicated they have an interest in the ATV. I guess they could be dumb but that statement doesn’t suggest a line of credit but a lien.
Credit card = unsecured line of credit. Totally different than a secured loan.
^^^ From the OP. It’s a secured loan.
It’s funny that one would even have this thread assuming they know a lien exists.
My concern is the bank or OP may be confused or guessed about if there is, in fact , a lein.
Very possible.