NEW ROCHELLE (CBSNewYork) – Three times this week, employees at a suburban hospital have encountered a very unpleasant surprise.

They’ve returned to their cars after work to find them vandalized, the catalytic converters literally cut away from the exhaust system.

On Tuesday, lab technician Jennifer Mendoza walked to a Montefiore New Rochelle Hospital employee parking lot, got into her SUV, turned the key, and heard something as unpleasant as it was unexpected.

“It was sounding like a Harley Davidson, boom, boom, boom… a big noise,” Mendoza told CBS2’s Tony Aiello.

Someone had crawled under her car and, using a saw, removed the catalytic converter, which is part of the exhaust system.

“It’s not the converter they’re interested in, it’s what’s inside the converter,” said Roger Morris of the National Insurance Crime Bureau.

Morris says there’s a black market for the catalytic converters, which contain platinum. Crooks can sell them for about $200 each.

New Rochelle police say three vehicles in the Montefiore lot had their converters stolen this week.

“What did it cost you to have it fixed?” Aiello asked.

“Seven hundred and fifty dollars,” Mendoza said.

“That’s a lot of money,” Aiello said.

“Exactly. That’s my paycheck,” said Mendoza.

Employees say the hospital has known about security problems in that parking lot for some time. In fact, it was reported to them in Dec. 2013, Aiello reported.

That month, five vehicles in the employee lot were broken into: Windows smashed, credit cards and other items looted.

Now there are catalytic converter thefts.

In a statement, the hospital is calling employee safety “a top priority” and promising increased security cameras.

Mendoza says she loves working at the hospital, but she’d also love to park her car securely.

The National Insurance Crime Bureau says catalytic converter theft has been growing since 2009. Almost 4,000 are reported each year. The bureau says many more go unreported.