Video clips from across the world have captured a sinister-sounding noise coming from the sky.
But no one can explain what it is.
The footage, from Germany, Canada, the USA, Ukraine and Belarus reveals similar sounding trumpet-like noises.
See a video here:
The first came from Belarus in 2008, while in the same year ear-defeaning sounds were posted to YouTube by an anonymous user.
And in June 2013, Kimberly Wookey. from British Columbia in Canada, recorded several noises coming from the sky.
A child apparently frozen to the spot after hearing the noise
Since then she has captured several more examples, with the most recent one being on May 7.
She wrote: I personally do not believe this has any religious connection, nor do I believe it is aliens, graders, trains, construction, etc, she added.
I do believe it could be a geophysical phenomenon.
Aaron Traylor, from Montana in the US, wrote: Ive had vivid nightmares ever since I posted the very eerie strange sounds that has Missoula talking and looking towards the sky; awful, awful nightmares.
My wife woke me from a dream last night where she says I was screaming like shes never heard me scream before.
I was taking my daughter out for her daily exercise along with my dog. I started to hear the sounds early on in our little adventure and the first time it was heard my dog perked her ears up and my daughter stopped in her tracks.
But what is it?
According to NASA, it could be the earths background noise.
A statement from the agency said: If humans had radio antennas instead of ears, we would hear a remarkable symphony of strange noises coming from our own planet. Scientists call them tweeks, whistlers and sferics.
They sound like background music from a flamboyant science fiction film, but this is not science fiction. Earths natural radio emissions are real and, although were mostly unaware of them, they are around us all the time.
What are these strange unexplained noises from the sky?
Angel farts.
Why is democracy held in such high esteem when its the enemy of the minority and makes all rights relative to the dictates of the majority? (Ron Paul,2012)