exhaust smell in the car

What is your question?

My 92 Camry with only 90K miles smells like exhaust in the car; the smell comes through the vent when the fan is on. Exhaust system, including catalytic converter is new and no exhaust leak has been found by 4 different mechanics including 2 dealership service departments. It is really bad and gives me a headache after driving for only 10-20 miles. There is no hole in the car, floor, etc. I am totally lost as what may be causing this. Engine light is not on; so all the computer codes are normal. Please help