It is 3am, and the village of Woodland is asleep. Up here on the fellside rising above the rugged beauty of Teesdale shortly before a summer dawn, all is dark and all is quiet.
Or at least it should be.
Two months ago, local people began to talk – discreetly at first – then with growing conviction about what they thought was a loud hum permeating their homes and the surrounding countryside.
Although descriptions varied, most of those that have heard it agreed it resembled a low-pitch throbbing which can strike at any time of day but appears to reach a crescendo in the early hours of the morning before abruptly ceasing as the sun rises.
It has been blamed for shaking the furniture, rattling conservatories and ruining sleep. News of what has become known as the "Durham Hum" has rekindled memories of previous sonic disturbances that have periodically haunted communities across the world, most famously the Bristol Hum which made international headlines in the 1970s. Events here have similarly aroused global curiosity and proved a fertile ground for internet conspiracy theorists, who have blamed everything from power lines to secret government activities or – even more fantastically – aliens.
But as I cock my ears and slow down my breathing in the pitch darkness, all that can be heard is the wind blowing gently through the trees and the sudden flapping of wings as a disturbed owl looms over a dry stone wall. After 30 minutes of intense listening, I give up and go home. The only hum I can record is of an olfactory variety emanating from a field recently spread with slurry.
Yet in this case it seems not hearing is not necessarily disbelieving. In the morning I meet retired store detective Marilyn Grech, 57, at her cottage. She has been up until the early hours, giving interviews to international radio stations, although ironically it seems the previous evening was the first time in six weeks that she has not heard the hum. "Last night when I got into bed I thought, this is fantastic, this is wonderful. This is how it should be," she says. Having moved into the village four years ago from Sunderland with her Maltese husband, Mario, 67, she admits she was anxious about going public – fearing she would be branded a "crackpot".
To her relief, many others agreed they too had heard the unexplained rumbling. Some said it has been going on for years. Since the publicity, a number of other "victims" of the sound in surrounding communities have also come forward. She admits she is sensitive to noise – Mario, who is partially deaf, concedes he has never heard it – but she provides a vivid description of what she hears. "It is a humming but it's got a bass – a heart beat going ba boom, ba boom, ba boom. Last Sunday it was so loud. It just pressurises up. The conservatory vibrates and it seems louder inside the house, although the hum is coming from outside. It is annoying and very irritating," she said.
Having initially thought it was a tractor's diesel engine left running, the couple went looking for the source. They couldn't find it. When she stuck her fingers in her ears it went away. Having contacted the local authority to raise the issue, she is awaiting the arrival of specialist recording equipment to try to capture the hum once and for all.
In the meantime, she can only speculate on the cause. "I am open minded and I am level-headed. I'm trying to get the simple things out of the way first – the generators and the tractors," she says.
"There are two sorts of people in the village. There are those who say they have definitely heard it and those who have never done so."
Firmly in the former camp is Michelle Fail, 43, whose family has lived in the village for more than 60 years. Despite being a paranormal investigator, whose garden is adorned with coffins, gargoyles and even a plastic severed arm, she believes there is a more earthly rationale for the noise. "There will be a logical explanation for it. We need to eliminate all the obvious causes but I am sure it is not a paranormal event," she says. "It sounds like something mechanical like a tractor but without the chug, chug, chug. It is just one drone," she adds.
At first she and her husband believed the sound was coming from their boiler. Then they thought it might be coming from their electric sheep fence. Now they think it could be something to do with the labyrinth of disused lead and coal mines which have pockmarked the landscape since medieval times.
Dr Geoff Leventhall, an expert in noise and vibration who has been investigating similar hums for 40 years, admits he has never heard the sound himself, although he did capture it on tape once. But we should never dismiss them, he says.
"If people say they have a noise problem then they have a noise problem. It is unfair to suggest otherwise. But what might be the cause of it we are not always sure."
The decibel level of a complained-about sound, he said, is often just on the threshold of human hearing. Typically 50 per cent of the population might be completely unaware of it. The likely sources of the Woodland hum are diesel generators, fan units – possibly two working in unison – or compressors, he says. Often a more effective way of dealing with unwanted noise can be through cognitive behavioural therapy, a strategy being piloted by the Government.
Experts have found that people are more antagonistic towards a sound they don't like the source of – such as a wind turbine or a motorway – compared to an equally loud babbling brook or the dawn chorus.
In Woodland, Angela Watson, a 49-year-old care home worker, clearly remembers the day she first heard the hum. "It sounds like a helicopter hovering above you but a bit bassier. It's in your face – it's not an ordinary noise," she says.
"I am the doziest person in the world but even I heard it last Saturday. I think it's the mines. Someone has been building something and dislodged something – unless it's a UFO come to take us away."
Other notorious sounds
Since it was first reported in 1979, more than 2,000 people living in the city have complained about the distant rumble, which continues to affect locals to this day. Among several explanations put forward are tests being carried out at the Rolls-Royce factory in nearby Avonmouth and the sound of traffic on the M32, which was fully opened in 1975.
Described as a combination of a truck engine and an industrial fan, the mystery noise was infuriating residents in Australia's normally laid-back surf neighbourhood (below middle) in 2009. The source remains unknown.
Auckland North Shore Hum
In 2006, academic Dr Tom Moir managed to record a sound which had been troubling locals in New Zealand's largest city. He later posted the audio file on the internet. Dr Moir has suggested using a CD of rain falling to help those whose sleep is affected by the hum.
Locals in the New Mexico town in the US have put up with an unexplained low-frequency noise since the early 1990s. Many suspected the sound emanated from US Navy stations. The phenomenon achieved international recognition when it was featured on the TV show The X Files. Despite a number of studies, the source has never been located.
A persistent humming on the Big Island has been blamed by locals on volcanic activity.