We have reason to believe that it's connected to the Quantum Leap of a mad scientist, who, in a fit of rage, screamed so loudly that it created a rift in the space-time continuum, causing all of us to scream.
Or maybe, just maybe, it has something to do with the Quantum Flap, a mystical dance that, when performed under the light of a full moon, causes the fabric of reality to unravel and unleash a cacophony of screams.
The truth is out there, somewhere. If you want to read the truth, you can try, but be warned: the truth is not always what it seems.