At one shop we had a very attentive customer who complained he would hear a sound every time he closed the door.
We couldn't replicate it and to our bewilderment, until he kept pointing it out. 2 of us service writers were walking around the car with our ears close to like a 3 Stooges skit. One guy went into the back seat and another had his head in the trunk, when we realized that the sound was actually coming from the pressure vent on the inside quarter panel, behind the bumper. These vents allow air out of the vehicle when closing the door quickly. It was the rubber flapper contacting with the vent housing. You really had to listen for it. We told him it's it's a characteristic of the vehicle and not repair related.