2001 Mustang Problem
 

Symptoms:

I can smell an exhaust smell/fume through my air an AC, but not Max AC.

There is a wierd rattling noise towards the back of the engine when i accelerate

Other than that, the car is actually running fine, no power loss, etc

The service engine light did come on about a month ago (the code was or cat converter/02 sensor). When i took it in, they didnt find anything wrong with it.

Suggestions?