With you guys talking about an exhaust leak, I got to thinking...
The car was rear ended when it was 1 year old, and the left muffler had to be replaced since it was smooshed under the car. I wonder if something is loose somewhere else along the line. It's quiet though.
It's either that or like said, the cabin vents that will be covered by the bumper cover to the rear of the rear wheels. Vent flaps missing or wedged open somehow.
They're supposed to let air pressure out but not in.