Well, second time I'm writing this. Lost the first very lengthy post because I neglected to log in. Oh well.
Basically, I think that this is a design/engineering flaw. I am starting to think that it actually has to do with the way the wind is blowing -- if the exhaust from the tail pipes gets blown under the car, it then travels up and gets sucked into the cabin air intake. If the wind is cooperating, there is no problem. This problem never happens when the climate control air system is off, so cabin air has to be actively sucked in, the air system must be turned on, to smell the exhaust fumes. Possible solutions: put an air cleaning pre-filter onto the cabin air intake. Or, direct the exhaust tail pipes upwards so exhaust can't go underneath so easily? Or, put an accessory fan into the exhaust system to increase the speed of the exhaust coming out of the pipes, to prevent it from drifting backwards so easily. Anyway, we'll be taking the car into service, but, I really don't expect a solution to this anytime soon.