Scientists have discovered the source of the mysterious humming sound that had been heard around the world. The anomalous seismic hum was first picked up back in November 2018 and was thought to have originated near Mayotte - a small island between Madagascar and Mozambique. At the time, it "triggered the curiosity of the scientific community" owing to the fact that it seemed to ring at a single ultra-low frequency and circled the planet without any sign of an earthquake. More than 400 instances of the hum were picked up by seismologists across the world. The culprit was finally revealed when, a few months later, it was discovered that a new underwater volcano had formed off Mayotte, pushing the island several inches to the south-east. A French oceanographic mission later revealed that the new volcano was absolutely huge - measuring 3.1 miles across and 0.5 miles high - however it still wasn't clear how it had produced the hum. Now a new study has finally lifted the lid on the mystery