Right, presurizing the inside of the car should decrees the amount of exhaust sucked in. You may be causing a venturi with the leaking sunroof. The air going across the roof is more than likely sucking air from inside your car causing a slight vacuum. At that point air is sucked into the car thru all the leaks. When My sunroof is tilted up, I can feel the air coming in thru the door, around the speaker, around the window switches...
Bill, 2003 3.5 SE Altima, Black with black leather, headers, full SS exhaust, lowering springs, adjustable shocks / struts, SCAFII, 20" wheels, SER Tail lights, Dual Halos around headlights, HID headlights and driving lights, Maxima Helical LSD.
2010 Maxima SV Prem + Tech package
2006 Vulcan 900 Classic