A series of mysterious booming sounds are being heard around the world, leaving experts stumped as to what’s causing them.

As many as 64 thumping noises have been heard everywhere from the Middle East to Cairns in Queensland, with the latest coming this week in the US state of Alabama.

"Loud boom heard: we do not see anything indicating large fire/smoke on radar or satellite; nothing on USGS indicating an earthquake,” the Birmingham National Weather Service tweeted following the noise.

Theories attempting to explain the startling sounds include sonic booms, military exercises, earthquakes and meteors – but there has been no confirmation as of yet.

View photos A sound graph from the USGS Lakeview Retreat in Alabama shows a loud boom. Source: USGS More

On October 10, a similar sound left Cairns locals baffled.

A FA-18 Hornet plane was heard flying over Cairns the previous night, but that is not thought to be the cause.

Just two weeks later, another boom was heard over the Eyre Peninsula in South Australia at the same time a blue meteor passed across the sky.

“It just got bigger and bigger and it was just this big flash across the sky and there were sparks coming off it,” Port Lincoln local Lisa Watson told News Corp.

“I pulled up home and I heard two massive bangs, maybe a second apart, and then the sky lit up again… I just felt the whole earth shake twice.”

View photos A bizarre flash of green light falling from the sky in Canada has been captured on video but no one is sure exactly what it is. Source: CBC News More

Over in Wales, there is again no explanation for a series of booms heard on May 11.

“It nearly gave me a heart attack it was that loud. At first I thought it was shotgun blast or a firework, but it was way too loud for that. It sounded more like a tank going off,” One Abergavenny resident told local media.

“My husband said it was probably mini meteors colliding with the earth, but have you ever heard such nonsense?”

NASA's meteor scientists are continuing their investigation in a bid to determine what has caused some of the noises.