For those that leave their helmets on the ground at stops.
The noise you hear may be your screaming or cussing, depending on what creepy crawly got in it.
My first experience with fire ants at Maxwell AFB AL was an eye opener. My helmet wasn't on the ground, but my butt in shorts was (working on my CB 750). I was the star of my own dance contest (only a 1 for style, but a 10 for exuberance).
You don't even have to leave it on the ground. A wasp or yellow jacket somehow got behind my face shield while I was riding several years back. It stung me 2 or 3 times before I was able to stop safely and get the helmet off.