(WTNH) – Catalytic converter thefts are happening across the state at an alarming rate, and if your car is targeted, it can be quite costly.

The most recent cases turned up in Plainville, Middletown, Milford, and Bristol. But what exactly is a catalytic converter?

It’s part of the car’s exhaust system that converts toxic gases from an engine’s emissions into safe gases. If it’s stolen, you will know immediately. As soon as you start your car and hit the gas pedal, you’ll hear a loud roaring sound.

The big question is why are they being stolen? The National Insurance Crime Bureau lists three valuable metals inside converters: platinum, palladium, and rhodium. Rhodium is reportedly the most expensive metal in the world at more than $2,700 an ounce.

Watch the video above for the full segment.