It was described as sounding like anything from a bomb going off to an earthquake.
But the loud bang heard over parts of Derbyshire this morning was actually the sonic boom from an RAF fighter jet.
Two RAF Typhoon jets from RAF Coningsby in Lincolnshire were scrambled to intercept an Air India Boeing 777 flight which had reported a security alert.
Flight AI191, which was heading from Mumbai to Newark New York, was diverted back to Stansted Airport where the passengers were safely disembarked.
But at around 10am today, no-one on the ground really knew what was happening.
(Does nobody remember what it was like when Concorde used to break the sound barrier when it went overhead?)
All they heard was a big bang or boom.
And for those who missed it, the video below shows what it sounded like. (The boom is at 13 seconds.)
The video was taken by Claire Murray at her home in Breaston. She posted it on Facebook saying there was the 'loudest double bang' and 'the house shook'.
The runway at Stansted has reopened and is fully operational.
