Mystery continues to surround a night time noise heard in the skies above Derry.
Last week SDLP MLA Pat Ramsey expressed concern over the noise which is keeping people right across the city awake at night.
“I have received a number of calls from concerned residents who have been unsettled and whose sleeping pattern is being affected by what can only be described as a relentless and disturbing buzzing noise in the Derry sky over recent days,” he said.
Mr Ramsey has since said he intends writing to the north’s Secretary of State to help solve the nocturnal noise mystery.
That move comes after City of Derry airport ruled out any commercial flight activity after 8pm.
The British Army, and the PSNI have both declined to comment on the source of the noise.
A spokesman for the MOD said: “As a matter of routine we do not discuss specific movements of aircraft.
“There is a formal complaints procedure in place with a 24-hour number available.”
A PSNI spokesman said: “The PSNI can only comment on the use of the police helicopter which is routinely used to prevent and detect crime and keep the community safe.”
Police have also not confirmed if an investigation is underway into the source of the noise or reveal how many complaints they have received in recent weeks.
Local people have taken to social networking sites to share their own ideas on where the noise emanates from - with many convinced it comes from the use of uav’s, or unmanned aerial vehicles, mini drones used by police forces as part of surveillance operations.