Residents across Cardiff and the Vale of Glamorgan reported hearing a "big bang" on Thursday evening. People living in Caerau, St Fagans, Culverhouse Cross, Cowbridge, Barry and Gabalfa reported hearing a loud noise from their homes on Thursday, May 4.
Speculation arose among residents as to the cause of the mysterious noise with ideas from thunder to terrorist attacks. However a spokesperson for South Wales Police says that they know what was "most likely" the cause for the disturbance.
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South Wales Police issued a statement on Thursday evening warning residents of Cardiff that H M Forces would be holding a training exercise at St Athan Airport, Cardiff. They wrote: "Local residents or people passing through the area may notice and hear increased noise."
South Wales Police wrote: "A pre-planned training exercise is being held today - Thursday May 4 - by H M Forces at St Athan Airport, Cardiff. South Wales Police is supporting this routine exercise. Exercises such as this are regularly carried to test contingency plans and the co-ordination of responses to major incidents.
"Local residents or people passing through the area may notice and hear increased noise. Risk assessments have been undertaken and we expect disruption to the public to be kept to an absolute minimum. This exercise has been planned for some time. It is not in response to any recent incident, intelligence or threat. The threat from terrorism remains at substantial, which means an attack is highly likely."
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