They are similar to sounds produced by a gun or cannon, rattle windows and doors but remain a mystery for scientists and witnesses.
Depending on which part of the world these noises occur, they go by a variety of names including mistpouffers in Belgium and The Netherlands; brontidi (or bartulio marinas) in Italy; barisal guns in England and Bangladesh; retumbos in the Phillipines; seneca guns in North America; seeschießen in Germany; and uminari in Japan.
The sounds are often, but not always, heard around water.
Possible explanations include earthquakes, rock bursts, mud volcanoes, explosive venting of gas, storm-driven waves, tsunamis, meteors, collapse of underwater caves, large waves crashing upon the coast; distant thunder and even singing sand.
There’s currently no scientific consensus as to what causes these noises.