"It's 11 o'clock in the morning and I'm suddenly aware of this buzzing, pulsating noise..."

That's how our investigation begins into a curious noise that has been reported by thousands across the world.  Following science reporter Linda Geddes in her journey to trace the source of the mystery noise, we explore the possible origins of a sound that has been reported from Bristol to New Mexico.  A trick of the ear, the hum of a city or sub-sonic secret military communications?  Listen... there... barely perceptible.  Do you hear it?

CREDITS

Reporter & script - Linda Geddes

Producer, camera, edit, sound & motion graphics - Adam Proctor

Click here to view the original feature at BBC Future

(Adam produced and shot this video during his time leading the multimedia unit at BBC Global News.