It is a question which has puzzled both experts and early risers alike – just what caused the strange high-pitched noise heard over Norwich?

https://infogr.am/mystery_noise-098

The loud screeching sound was reported across large parts of the north of the city for around 30 minutes in the early hours of Monday morning.

People on Crome Road, The Erins, Dibden Road, Silver Road, Bell Road and Denmark Road and Cottinghams Drive in Hellesdon, all said they heard the high-pitch sound.

Yet despite inquiries to find out what it was, nobody knows.

Everything from an alarm at a nearby factory to an alien invasion have all been suggested, yet a weather expert, airport boss and the general public remain baffled.

Aviva trainer David Allison, 29, of The Erins, captured the sound on a video.

He said: 'I have never heard anything like it and it definitely wasn't an alarm. At just gone 5am there was a horrendously loud high-pitched noise outside. I witnessed this just off Denmark Road and my colleague also witnessed it on Bell Road. It lasted for approximately half an hour before making a 'powering down' noise, it then started again approximately 20 minutes later for another 10 minutes.'

One suggestion was it was coming from the Van Dal shoe factory on Dibden Road, either from an alarm or a piece of machinery.

But Jason Larke, Van Dal marketing director, said they had no log of an alarm sounding and that the factory would be shut down at that time of day.

He said the company would look into the noise but added: 'It doesn't appear to be something on the site.'

And forecasters did not see any change in weather which may have created the sound.

Weatherquest's Phil Garner said: 'Nothing weather-wise would have caused a problem.'

Norwich airport's general manager, Richard Pace, said the airport was closed at the time the noise was heard, and knew nothing about it.

Philip Bray wrote on the EDP Facebook page: 'I heard it too as I work over on the White Lodge industrial estate in Lakenham.

'The only thing I can think of is possible alien activities since it was a powering down sound, didn't see any unknown aircraft – just heard that sound followed by it starting again.'