I got such an annoying metallic rattle noise on our lady as well. No stethoscope, no endoscope, nothing helped, noise came from everywhere. After a wile i found it by chance: We have a 1930 body and the hood can be fixed open with this part:
https://www.snydersantiqueauto.com/hood-prop-kit
Over time, the ends lost their rubber covering. This made my rattle. Re-rubbering with a tube made our lady nicely quiet.