Alabama -- The McCalla Hum

One day in late 2011, the residents of McCalla, Alabama, woke to a strange, unidentifiable noise. Variously described as "sirens in the distance," "locusts," or "whirring of a helicopter," no source could be found for the constant hum, even though authorities thoroughly searched the town. Even more baffling, witnesses say that when they walk toward what they think is the source of the noise, the hum grows dimmer in that direction and louder in the direction from which they came.