New Zealand is Droning

Apparently this sound (which I can only hear through headphones) is causing quite a stir in the northern districts of Auckland. The sound is so maddening, it seems, that it's inspired some residents "to take drastic action" – which, in one case, means purposefully deafening oneself with the roar of chainsaws.
In fact, "for those who can hear it, the sound is the bane of their lives."


The sound also reveals where unexplained acoustic phenomena, dishonesty, and urban real estate intersect: "Some have been reticent to give away more details of their predicament for fear that reports of persistent humming could adversely affect the resale price of their homes."
One of the researchers trying to locate the sound's origins "rules out geological factors. 'It's more likely to be things like pipes under the ground – you know, gas pipes, sewerage pipes, factories in the distance.'" CIA installations, perhaps.
"This is not the first incidence of humming in New Zealand," we're told. Oh, no. "In 2005, New Zealand author Rachel McAlpine wrote a book called The Humming... largely inspired by the author's own experiences in the seaside town of Puponga on the northwest tip of New Zealand's south island which was itself at the centre of a humming mystery some years back." That man was later arrested.
In McAlpine's novel we read how "life is becoming increasingly frustrating for [a character named] Ivan because he is plagued by an underground humming that he tries to disguise with an increasingly bizarre array of devices."
If it were my story to re-tell, however, Ivan would soon become so unbelievably good at manufacturing sonic camouflage that he turns into the terror of post-Blair Great Britain. (He moves to Britain). Completely silent, exploding noiseless weaponry over the city of Birmingham, Ivan's Joseph Conrad-inspired, acoustically avant-garde ransom demands are met not with payment stashed inside a pre-arranged safety deposit box – but by a visit from a certain, rather well-known, secret agent of the crown... Unfortunately, James Bond is almost immediately captured – having been dumbfounded by a house full of mirrored rooms, someone else's mobile phone, and a weird echo, coming as if from behind him, that induces a state of cognitive paralysis. Bond is then subjected to a series of unbearable noise-tortures, leading some in the audience to laugh and others to accuse the film of being an unacknowledged remake of The Ipcress File. But, once the enemy is brought back on screen, transformed by his life of sonic dissimulation, he addresses Bond through a grotesque series of hand-held voice-cancellation machines – and we see that something altogether more terrifying has been planned...
Of course, it has long been known that if you "listen carefully... you can hear the Earth singing quietly to itself."

They live underground. They are everywhere but seem to come from nowhere. They barely exist, but never leave. If sounds have shadows, they are the shadows of a sound. Researchers call them the background free oscillations of the Earth.

These "background free oscillations," however, while more or less totally unrelated to the New Zealand drone, discussed above, are also unexplained. This endless terrestrial resonance could be "buildings shuddering in the wind," for instance – or it could be "the constant throb of fluctuating atmospheric pressure all over the Earth." It could even be the combined effect of all the oceans' waves crashing on all the earth's shores simultaneously. It could even – though let me pull the blinds closed as I write this – it could even be the rumble of invisible stealth bombers breaking the sound barrier out at sea...

(Thanks, Marcus! Earlier: Sound Dunes, Dolby Earth, and so on).