I was somewhat awoken by a series of huge, bone-chilling, rumbling sounds at around 20 past Midnight on Dec 21st. It was similar to the distant rumblings of a thunderstorm, but the sound was more regular like the sound of flames. It sounded 4 times (or 5?) at what seemed to be equal lenght, about 5 seconds, and with equal intervals of about 5 seconds.
Was really astonishing... I thought this was a signal of the Apocalypse or something, so I almost panicked.