Has Bristol hum mystery been solved?
The Bristol "hum" which plagued residents across the city for years could have been ... nothing.
For decades, hundreds of people around the city said they could hear an elusive buzzing.
Some blamed power lines, some the M32 and others the factories at Avonmouth. A few even thought more sinister forces could be at work.
But most people said they heard nothing at all.
Business Cards From Only £10.95 Delivered www.myprint-247.co.ukView details
Our heavyweight cards have FREE UV silk coating, FREE next day delivery & VAT included. Choose from 1000's of pre-designed templates or upload your own artwork. Orders dispatched within 24hrs.
Terms: Visit our site for more products: Business Cards, Compliment Slips, Letterheads, Leaflets, Postcards, Posters & much more. All items are free next day delivery. www.myprint-247.co.uk
Contact: 01858 468192
Valid until: Wednesday, May 22 2013
Now, a hearing expert believes he has come up with the answer to the 30-year mystery.
Dr David Baguley, head of audiology at Addenbrooke's Hospital in Cambridge, estimates that in about a third of cases there is some environmental source for the hum.
But in most cases no external noise can be identified, he said.
Dr Baguley's own theory is that many sufferers' hearing has become over-sensitive.
He said people have an "internal volume control" that helps them amplify quiet sounds in times of threat, danger or intense concentration.
The Bristol "hum" made international news in 1979.
People living in Fishponds were convinced it was coming from heavy traffic on the M32.
Residents of Sneyd Park even petitioned the council, which sent out a team of environmental health officers who made more than 30 trips to various parts of the city in search of the source.
Conspiracy theorists were convinced the Government was behind the hum, broadcasting messages from secret research stations. Others were convinced it was all down to microwave transmissions or power station transformers.
Dr Baguley said: "If you're sitting by a table waiting for exam results and the phone rings, you jump out of your skin.
"Waiting for a teenager to come home from a party – the key in the door sounds really loud. Your internal gain is sensitised.
"This becomes a problem when an individual fixes on a possibly innocuous background sound, and this act of concentration then triggers the body's 'internal gain', boosting the volume.
"It becomes a vicious cycle. The more people focus on the noise, the more anxious and fearful they get, the more the body responds by amplifying the sound, and that causes even more upset and distress."
Dr Baguley is working on a pilot project with the acoustics laboratory at the University of Salford. The trial – funded by the Department for Environment and the Department of Health – uses psychology and relaxation techniques to help sufferers become less agitated and distressed by the hum.
Philip Robinson, 50, a consultant ear, nose and throat surgeon at Southmead Hospital specialises in hearing problems and knows Dr Baguley's work.
He has seen a handful of patients who have complained of the hum over the past 15 years.
He said: "People have a mechanism for controlling loudness. If you are asleep at night and a lorry goes past, your brain does not wake you up.
"But if you hear a tiny creak on the stairs you will wake up.
"People who hear noise constantly find it is worse inside houses and worse if they fit double glazing.
"There are definitely some cases where there is an environmental source but more often it's inside the human being."
"I believe that psychology and relaxation is the way forward in these cases."