Ok, take this for what it is worth. One day last fall I was driving in some pretty heavy wind with larger gusts. All of a sudden I heard a bang. Thought I had run over something. Got out and opened the hood and checked from top to bottom. Nothing. So I continued and again a few small bangs and then a large one. After awhile I looked at the slide topper on drivers side. Wind was hitting me on drivers side. It seemed tight. The banging continued but became less and I realized the trees were providing a windbreak now. I ran my mirror up so I could see the topper and tried to watch it without having an accident. Sure enough. When I cleared the windbreak I saw it with a gust. The topper was moving out an inch or two and banging back. I would have sworn the sound was coming from the front lower area. I suspect it is not your issue but lesson is not to confine your search to one or two things. Good luck.
