But she knew the noise her vehicle was making meant trouble of some kind.

It was the afternoon of July 8. “I went outside after work and started my SUV, and it sounded like 10 Harleys were just gunning it,” she said. “Obviously, I knew something was wrong.”

A mechanic who checked out Miller’s SUV found the problem right away. Someone had stolen her SUV’s catalytic converter. The device, which reduces the toxicity of emissions, contains metals that more thieves are discovering.

Across Johnston County, Miller is not the only victim of such thefts. Although hers is the lone case reported to Clayton police, Capt. John Gerrell said officers in Johnston and other Triangle counties consider the thefts a growing trend.

“We know that Wake County in particular seems to have a rash of these thefts from time to time,” Gerrell said. “It’s starting to spread around.”

Perhaps hardest hit by the recent thefts has been the Town of Benson, where police report that six cars were stripped of their catalytic converters in two days in June. Lt. Greg Percy of the Benson Police Department said the thefts occurred in parking lots outside two buildings on North Wall Street — the American Legion Post 109 and M&H Auto Parts & Service Center.

Percy said commuters use the Legion building parking lot as a park-and-ride lot. Whoever stole catalytic converters from three cars parked there had ample time to accomplish the task, Percy said. Drivers who park in the lot often arrive as early as 6 a.m. and don’t return until after 5 p.m.

Meanwhile, the person or persons who stole catalytic converters from pickups and sport-utility vehicles outside M&H Auto would have had to work at night, Percy said. In both cases, the vehicles targeted were larger models, he added.

“There’s a reason,” Percy said. “We’ve found that more trucks and SUVs are targeted because they sit higher off the ground and are easier to crawl under. A thief can probably take what they’ve come for on those cars within a couple of minutes.”

Lt. Keith Powell of Smithfield said police around the county had been somewhat baffled by the recent rise in thefts of catalytic converters. Six thefts have been reported to Smithfield police since July 1, he said. Four of the thefts occurred at a car lot on N.C. 210. The other two occurred in a courthouse parking lot and at Barnes Auto Parts on North Bright Leaf Blvd.

“I can’t remember ever really having another time when thefts like these have gone on,” Powell said. “We have had some [catalytic converters] stolen in the past, but they weren’t attached to cars at the time.”

Percy said thieves steal catalytic converters for the money they receive for selling the parts to scrap yards. Catalytic converters, which are made of platinum, can yield cash returns of up to $200, according to a recent Newsweek article.

Police said drivers could do little to protect themselves from becoming victims. According to Percy, alarm systems likely wouldn’t sound unless the thief was to shake a car violently while removing a catalytic converter.

But Powell said motorists could still exercise sound judgment in choosing where they park their cars. “The key is to be cautious, know your surroundings and check your car frequently,” he said.