

Edit: According to Wikipedia, the final stance now is that the wound was caused by a stray bullet.
No link provided, so I looked it up. It’s in the article Attempted assassination of Donald Trump in Pennsylvania, under Shooting (pretty deep in there though):
The upper part of Trump’s right ear was grazed by the first bullet Crooks fired.[99][100][101]



Sounds like popping bubble wrap, or popcorn.