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One possible explanation for "The Hum" is that the earth is actually a ball of molten iron, and we are living on the crust of slag that floats around on top.

This is true!

The movement of chunks of slag on top of the molten core is called "continental drift," and it goes on constantly. It is responsible for volcanoes and earthquakes.

For example, a big plate in the Pacific Ocean is slowly sliding under the western edge of the state of Washington where I live, and the slippage of these plates is the main progenitor of earthquakes in this area, and for the Cascade Mountain range, many of which, e.g., Mount St. Helens, are volcanoes (leakage from the earth's core).

This is an oversimplification of what's going on, but it gives a general idea. Terra firma ain't so "firma!"

This constant grinding of tectonic plates deep below our feet is responsible for all kinds of subsonic sounds, some of which may reach up into the audible range.

Such as the mysterious, but ongoing low-pitched hums that can be heard various places around the earth.

Yellowstone National Park actually sits in the caldera of a huge volcano, which is still actively boiling away deep underground. This accounts for the geysers and the boiling mud-pits. Geologists have said that the last eruption of this volcano occurred some 600,000 years ago--and there are serious signs indicating that a monsterous eruption is due at any time now. In fact, it's many centuries overdue!

That'll be quite a party! A volcanic eruption that big would make the eruption of Krakatoa in 1883, which was heard 3,000 miles away and changed the world's weather for several years due to dust clouds in the upper atmosphere, look like a minor hiccup!

That'll be quite a party!

Sweet dreams....

Don Firth