Islanders believe mystery humming is submarine-tracking sonar

Lauren-Grace Kirtley says the sound can leave her feeling dizzy

Islanders in the Outer Hebrides whose lives are being disrupted by a mysterious humming sound say they believe the source is military operations in the North Atlantic.

The persistent low frequency noise, reported by hundreds of people in the past few months, has been causing health problems and stress for people who can hear it.

Lauren-Grace Kirtley, who set up a Facebook group to try to help solve the mystery of the "Hebridean hum", said they now believed the sound was caused by military operations and could be heard along the Scottish coast.

However the Ministry of Defence said an initial assessment suggested the hum was not due to Nato military activity in the area.

Amateur investigations by islanders had pointed to Nato and Ministry of Defence (MOD) exercises using sonar technology to detect submarines.

Dr Kirtley, a medical doctor and university lecturer, said residents of Lewis started hearing the disturbance around the time that Nato and MOD operations were using new low frequency active sonar technology for submarine detection in the North Atlantic and the Minch.

"After excluding a lot of what we thought were local possibilities with infrastructure and things that might be causing the low frequency sound, we now have a high degree of confidence that that is what we have been listening to," she said.

Theories posted on the Facebook page included the cause being the motors within wind turbines, TV masts or tinnitus, a condition that causes ringing and other noises in a person's ear.

It was also suggested the noise of ferries operating between Lewis and the mainland could be carried on a persistent easterly wind.

Electricity company SSEN's Battery Point Power Station in Stornoway was ruled out as a cause early on because it only operated at certain times, while the hum was reported as a constant problem.

'Man-made sound'

Speak on BBC Radio's Good Morning Scotland programme, Dr Kirtley said the "hum" could be recorded with a spectograph and was consistent with location triangulation.

There had been an "evolution of the the sound" over the past six months and people had contacted them from "all coastal areas around Scotland" to report their experiences.

"It started as 50Hz constant hum, we're now seeing the addition of 100Hz, 150Hz, sometimes lower (20, 30, 40) sometimes constant, sometimes pulsing at very regular intervals," she said.

"It's very obviously a man-made sound and consistent with the use of sound for triangulation and for the location of objects. Not everyone can hear very low frequency sounds.

"But for a small but significant subset of the population, this is really affecting their wellbeing and their health and I don't think we can underestimate the human impact of being exposed to sound constantly."

The sound has been reported widely across the Isle of Lewis and beyond

She said the "intrusive" noise had led to health problems for some people, including headaches, migraines and insomnia.

"People have described it as torturous," Dr Kirtley added.

Islanders have tried contacting the MOD via freedom of information requests and through their parliamentary representatives.

She said: "As of yet we've had no response from them."

An MOD spokesperson said: "We have been aware of the issue and our initial assessment is that this is not being caused by Nato military activity in the area.

"We will respond to the parliamentary question and freedom of information request in the usual manner."

Sensors hidden in UK waters

Defence operations in the North Atlantic include regular training operations bringing together allied nations to work on anti-submarine exercises.

The UK is leading Project Cabot, Nato's anti-submarine warfare smart defence initiative, which will use uncrewed maritime systems and AI to strengthen undersea surveillance and defence.

The North Atlantic waters between Greenland, Iceland and the UK are considered to be a vital area for monitoring naval movements.

In a BBC interview in April, Russia's ambassador to the UK did not deny claims that Russia was attempting to track British submarines using sensors hidden in seas around Great Britain.

However, he rejected the idea that such activities presented a threat to the UK.

Low-frequency noise has disturbed residents in other places in the past.

Last year, it was suggested the source of a mystery humming sound which had plagued people living in Omagh, Northern Ireland, had been identified and dealt with.

Fermanagh and Omagh District Council said its environmental health officers had been able to "hone in" on a particular business.

Also last year, North East Lincolnshire Council said the source of a mysterious humming noise that plagued residents of Immingham may never be discovered.

People said they had heard the low-level sound for a number of years.

In 2013, New Forest District Council investigated reports of a drone-like sound heard on the south coast of England.

One theory advanced at the time was that it might be the mating calls of a certain species of fish.