This. There is a black plastic piece that goes between the door and the front door frame to prevent the door from closing on you when the car is not level or it is windy. If it becomes worn or damaged, it will make a popping or clicking sound. If you look carefully, you may even see that the very end of the plastic part that connects to the door frame is cracked where it surrounds the pin that holds it in place. These get damaged when the wind catches the door and it is over extended and cracks that plastic piece. It is a cheap part to replace but you need to remove the door panel to access the bolts on the door side. I have two that are doing that right now and because I know what it is and that they are still functioning for the most part, I am ignoring the noise. FYI, this is a very common GM part used on most of their cars.Very often, the pop sound when opening and closing the door is due to a faulty door check assembly. Replacing the door check is the usual solution.