A cruel con artist swindled an 86-year-old Queens woman out of more than $11,000 by convincing her there was a mysterious sound coming from her car that he could fix, authorities said.

Billy Thompson, 47, did nothing but fiddle with the engine of the elderly woman’s 1976 Dodge Aspen before taking her bank check, according to the Queens DA’s Office.

The woman was driving on Sept. 23 when she stopped at a traffic light.

Thompson approached, said the car sounded funny and offered to solve the “problem,” prosecutors said.

He popped the hood, acted like he was working, then demanded $13,000.

The woman managed to bargain him down to $11,200, and he accompanied her to a bank where she got a certified check, authorities said.

Thompson faces up to seven years in jail on grand-larceny charges.