Does it have 2 exhaust pipes in the back? Is there a badge that says GT or a coiled snake on the side of the car? If yes, then that means your car has a V8 engine, and it's supposed to be loud. You may have noticed the car accellerates really quickly when you hit the gas. No, it's not broken...
between these two, I'd go for the Camaro. The Challenger interior is too boring, and the Camaro is faster. Now, what I would really do is walk past them both and jump into a Mustang GT.