If the car is louder than what you are used to, you have a simple exhaust leak somewhere in the exhaust system. This begins with the exhaust manifold and ends at the tailpipe. Any exhaust leak along this system can cause exhaust gases to build up in the cabin. Even leaks from the muffler or tailpipe.
Your nose is a pretty good instrument. But it can’t smell carbon dioxide. In fact, you could very comfortably die breathing CO2, since even your blood would be fooled to believe that it is absorbing a nitrogen/ O2 mix (along with CO2) until you fell asleep and died.
You have an exhaust leak, and you are smelling exhaust. Fix that.