THESSALONIKI – It wasn’t the Twilight Zone or the X-Tapes, but must likely just a drop in pressure in underwater water pipes in one neighborhood of Greece’s second-largest city of Thessaloniki that awakened residents early in the mornings with a curious, soft, uneasy thumping sound.

It was eerie and unsettling, especially not knowing from where it came or whether it was a precursor of an earthquake but the belief now is that the pipes being checked by the city’s utility company is the culprit.

The sound set off theories from the scientific to the supernatural about what was causing it and drawing speculation from professionals to amateur sleuths as to what it was.

Geologists have ruled out natural causes, said Kathimerini and Vassilis Melfos, a geologist at Aristotle University who visited the area in the Pavlos Melas said he thinks it’s the pipes.

“The sound comes from a specific street, under which there are water and natural gas pipes. I would conjecture that it’s from the drop in water pressure at night,” he said. “I would rule out underground shifts because … such phenomena don’t follow a pattern,” he said.

Mayor Dimitris Demourtzidis said the natural gas company has checked and found nothing and that now it’s the turn of the Thessaloniki Water Company (EYATH), which was planning to run tests.

“I think the issue is with the water pipe because the sound we hear on Kifissias Street is the same as at the reservoir,” he said. “People are still worried even though a geological phenomenon has been ruled out, meaning that we know it’s nothing dangerous,” he also added.