From the University of Iowa:
Whistlers are produced by lightning and travel along Earth's magnetic field line from one hemisphere to the other, as shown in this illustration. In the ionized gas that exists in this region of space, the high frequencies travel faster than the low frequencies, thereby dispersing the wave from the lightning stroke into a whistling tone that decreases in frequency with increasing time, hence the term "whistler."
Hear earth whistlers here.
And here is an "earth chorus", which sounds remarkably like my parents' backyard on any given summer night.
Again, from U of I:
Chorus waves in Earth's magnetosphere are generated in the Van Allen radiation belts by electrons spiraling along Earth's magnetic field lines in this region. Once generated, the chorus waves interact with the moving electrons, disturbing the spiral orbit of the electrons and causing them to fall into Earth's upper atmosphere along the magnetic field lines.
Chorus waves consist of a rapid succession of intense ascending tones, rising in frequency over very short time intervals, each tone lasting typically less than one second. The frequencies of these rising tones occur in the audio frequency range and sound like a dawn chorus of chirping birds, a sound which gives these waves their name.