I have noticed an intermitent exhaust smell in the cabin, even with the A/C on, when idling around other cars - at stoplights, for example. I thought at first that it was my own exhaust leaking, but when I took it to Midas, they couldn't find anything, and of course there was no smell. Is there some sort of filter that should keep out such smells on the car somewhere? The car is a 2000 3.2 ES, 142K miles, with new head gaskets, new A/C.