You know, I had a Scirocco that did some strange things. I had damaged the car in a way that popped some of the spot welds around the front right wheel well.

No visible damage at all. But on a hunch I had somebody else bounce the fender, while I laid a hand over various seams/joints in the sheet metal. I found one that breathed open and closed. I could feel it but it wasn't easy to get a sight on it.