What the researchers still haven't figured out, they concede, is "how the auroral sounds are created."
They add that:
"The recorded, unamplified sounds can be similar to crackles or muffled bangs which last for only a short period of time. Other people who have heard the auroral sounds have described them as distant noise and sputter.
"Because of these different descriptions, researchers suspect that there are several mechanisms behind the formation of these auroral sounds. These sounds are so soft that one has to listen very carefully to hear them and to distinguish them from the ambient noise."