In the late 1950's, scientists accidentally discovered something that wasn't meant to exist; it was dubbed the "Frequency".
The "Frequency" works on a basis that prolonged exposure increases the signs of the symptoms of paranoid anxiety. For example, somebody who was exposed for ten minutes would have less indications than a person exposed for one hour.
This "Frequency" was kept a secret; should it be revealed, quite a bit of hysteria could be stirred up.
Naturally, the scientists responsible for the Frequency felt it necessary to test its effects on humans.
The first test, which lasted about twenty minutes, showed no immediate effects... with the exception of some acute anxiety.
Test two lasted two hours long. After going past the twenty-minute mark, the subject seemed anxious, as observed in the previous test. For this test, the scientists took extra measures and strapped the subject to a chair.
The test continued.
After forty-five minutes have passed, the subject seemed agitated... they stated that they were being bothered by some kind of "fog" in front of their eyes. We acknowledged the individual's discomposure, while at the same time, took notes on the effects of the "Frequency's" inducing symptoms.
One hour and fifteen minutes on the timer, the subject appeared more distressed. The subject was constanly moaning and whining, while showing signs of delusion. The subject constantly darted his head around the soundproof room at random intervals.
About twenty minutes later, the subject began to weep. When questioned by one of the scientists, he complained that these "shadowy figures" were standing in the "fog". It should also be mentioned that the subject stopped moving around to stare at the wall the chair was facing.
Fifteen minutes left on the timer. The subjects suddenly broke into full panic-mode. They started rocking, and making frantic facial gestures towards the scientists, begging them to end their suffering. They were constantly blathering that the "shadows" were walking out from the "fog", and that they were going to "take them".
Thirty seconds left to tick away. The subject's spastic movements freed them from their prison. They sprinted out of the test room. Before the scientists could stop them, the subject snatched a scalpel from a surgical table and grabbed the scientist nearest to him. The subject proceeded to drag the blade across the scientist's throat, ending their life. The subject then dug the scalpel into his own eyes, and removed them from their sockets, in an attempt to rid himself of the images.
Naturally, the tests were scrapped and the research was buried deep in the archives.
I put your life at risk by waiting this long to tell you. You see, the so-called "Frequency" is a low and loud hum, one can not listen to it for too long.
Although it's probably too late, considering the time you've been on this site, trying to scare yourself. You're soon to experience what real fear is.
Let's review the facts, it is generated in a place which would cause mass panic if discovered. It makes you feel fear and anxiety, and makes a low, loud hum.
All seems pretty damn inconclusive to me. But, wait... what's that sound coming from the device you are reading this on?