A mysterious humming driving people to despair across Auckland has pricked the ears, and curiosity, of scientists trying to find the source.
Massey University computer engineering scientists Tom Moir and Fakhrul Alam have been contacted by more than 30 people, most in Auckland and the North Shore, who claim to have heard a humming noise.
The symptoms are similar to those suffered by people with tinnitus, commonly associated with a prolonged high-frequency ringing in the ear.
The scientists are visiting people who can hear the humming, and trying to measure the noise in the hope they will be able to identify its source.
People from central Auckland to Kaiwaka in Northland have reported the sound, as have residents from the North Shore suburbs of Torbay, Browns Bay, Murrays Bay, Birkenhead and Beach Haven, and Stanmore Bay on Whangaparaoa.
The scientists are measuring the frequency by playing a second low frequency to someone who can hear the humming. When the person can no longer hear the hum, the frequency they are playing is the same as the humming noise.
Dr Moir said people could definitely hear a sound. "It's quite serious to them, it's driving them bonkers. I was there at the same time and I couldn't hear anything."
He said the sound was well within the average hearing range for people.
Most people can hear between 20 hertz and 20 kilohertz and the humming is around 56 hertz, according to Dr Moir's research.
Not everyone could hear the sound, because of its low volume, he said.
"We're all born differently - some people are better runners, some people are better hearers."
An Auckland woman who heard the sound described it as a "low drone or rumble".
The woman, who asked not to be named or have her suburb identified, said the noise had become so bad she was thinking about selling her home.
"I absolutely love my home but last night I couldn't get to sleep before 5am. In desperation I even tried to put Blu-Tack in my ears," she said.
But nothing works. The noise is louder inside and during the night when there are no other sounds to mask it.
The woman said there was no point telling people who could not hear it because they thought she was "stark raving mad".
The founder, patron and counsellor of the New Zealand Tinnitus Association, Joan Saunders, said some of the people who contacted Dr Moir did have tinnitus, but not all of them.
She could not diagnose everyone without meeting them, she said.
Dr Moir could not hear the sound himself but his wife, Jude, could.
She described the sound as an "awful noise and sensation".
"It feels creepy. It's not a place I'd like to live regularly," Mrs Moir said.
Author Rachel McAlpine based her 2005 novel The Humming on her experiences of a mysterious humming in Puponga, near Farewell Spit.
The book featured an unknown humming noise that plagued only certain people in a small town.