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Lauren-Grace Kirtley, who has set up a Facebook page dedicated to the "Hebridean Hum", said about 200 people on Lewis have reported hearing the noise.

Trump's mother was born and brought up on the Hebridean island of Lewis.

On the west side of the Hebridean islands is the North Atlantic, with nothing but open ocean until North America.

They've been on group holidays to Fontainebleau, a climbing hotspot in France, and cycled the Hebridean Way with their climbing friends.

Soon they were dating - and the following year, sitting on the observation deck of Hebridean Isles on a glorious summer's morning, he asked her to marry him.