North Wales booms due to HMS Montrose warship exercise
Residents in north west Wales might have been forgiven for wondering if they were coming under bombardment when a series of loud bangs rocked the air.
Police and emergency services reported calls on Monday afternoon from a number of concerned local people.
North Wales Police and coastguards confirmed the source of the booms was a warship exercise near Tywyn.
One resident in Criccieth, Gwynedd, said the sound was so loud it registered on home recording equipment.
David Tuffnell has a home recording studio and was trying to record some harmony vocals when the bangs started at about 13:00 BST.
He told the BBC Wales News website: "The bangs have been reading on the meters here and I heard them as well.
"Every 20 minutes there are noises and they seem to be in a sequence of about five or six each time.
"It's very disturbing. Homes here in Criccieth are shaking.
"I think it would be a bit frightening for elderly people. Some who are sunbathing here have said to me they felt quite dizzy hearing them as you can feel it, like a bass boom in a nightclub."
Other people took to Twitter to report the noise, variously described as like thunder, sonic boom or seismic-like activity, and some said it caused the ground and walls to shake.
The ship, the HMS Montrose, is currently undergoing preparations for deployment later this year.
Anyone wanting to register a complaint should call 0800 0510880.