Yep, you heard right. As Earth goes whizzing and whirling around the sun, it hums. If it were several octaves higher - we'd be able to hear it. But the Earth hums notes too low for human ears. It's a mystery.
Scientists know that sound waves in the atmosphere correspond to similar waves underground.
What gets the sound waves started could be changes in air pressure, or maybe the pounding of ocean waves. Some scientists think our two closest cousins Mars and Venus might be harmonizing along with Earth.