I looked at a few GN restoration pics and there were locations that would have just taken a ton of body filler and smeared it across the hood and taken the long pneumatic sander and worked it smooth, primer and painted it. I being the novice kept playing with it not realizing that between the hood and the bracing on the bottom is a hard sealant that is a body panel adhesive substance. It is the bond between the two panels of the hood.If that bond is ever broken for whatever reason it will create a "tin can effect". Basically when you press down and release you tend to hear a pop. As I was sanding trying to get my body filler smooth, I was pressing a little too hard ( the sheet metal on the hood is actually very thin) killing my high spots, making them my new low spots. So I would apply more filler in that area and do it again. I fought this thing for several weeks until I flipped the hood over and put some adhesive between the brace and hood. It was easier for me to sand all of the body filler back off and start over. What??