The ugliest noise I've ever heard that has nothing to do with technology came out of a pig's mouth. Agitated pigs make a lot of noise, and it's horrifying. It sounds stupid to say it's horrifying to hear a pig squeal, but wait 'till you hear it. It's so loud, and visceral, and just ugly. It sounds like something is getting tortured.
In Nicaragua (where I served an LDS mission), people just randomly keep pigs. Oftentimes they butcher their own pigs. When those pigs know the knife is coming…when the squeal crescendos, then sharply cuts off…sheesh, I'm creeping myself out. It's almost worse to write about it than it was to be there.
Or, how about a man's angry scream, followed by running footsteps and the sound of something repeatedly striking flesh? Heard that in Nicaragua too, sitting in someone's (fenced-in) yard. By the time we got to the gate, there was a crowd in the street but we didn't see anyone hurt. I still don't know what happened. Not a happy moment, that.