catalytic converter noise

2013 Kia optima 43k miles. The car has a loud tick/ping from the cat. conv. begining just after the car is warm(2-3mins). and continues several minutes after shut off. No external damage, but noise is a lot louder than normal. I know thy can make similar noises to a much lesser level, but this is audible from across a parking lot. How do I tell if it's going bad prematurely?? What is considered normal/acceptable noise levels?