When I was 20, I was quail/rabbit hunting with my buddy. We were on public land. As we came up over the top of a gentle hill, we were about 20 feet apart, he was in front. We both heard a "wzzzzz" sound, followed quickly by boom. I shouted and my buddy shot his 20 gage straight up into the air.
Turns out some clown was sighting in his 30-06 by shooting soda cans and jelly jars, and he was not very careful about his backstop... He was only about 150 yards away.
The wzzzz sound was sort of like a horse fly buzzing past my head, but louder. It moved VERY fast from left to right.