With his Mister Softee ice cream truck parked in a familiar spot, its presence announced by a sprightly metallic jingle, Costas Vamvakas was having a good day on Wednesday, the holiday business brisk despite the drab weather. But then two men pulled up in an unmarked car from the Department of Environmental Protection.

It was Mr. Vamvakas’s first encounter with the city’s noise police, a contingent that includes 45 environmental agents and thousands of regular police officers who are enforcing a sweeping new noise code that took effect on Sunday. Mr. Vamvakas, 24, who is part owner of a Mister Softee franchise in Queens with 11 trucks, had failed to turn off his truck’s jingle when he parked at the curb, as is now required of all ice cream trucks.

The fine is $350.

Mr. Vamvakas, who is known as Gus, recalled the encounter, which took place in a parking lot at Fort Totten Park in Queens, in an interview yesterday during a break from his Flushing rounds. He said he told the two agents that he would lose business if he turned off the jingle.

“I am aware of the law, but I need to play” the jingle, he recalled telling the agents. He said he pleaded with them: “Can’t I play it for 10 seconds while I’m stopped?”