Petra,
As a science teacher I had students chew a wintergreen lifesaver in front of a bathroom mirror in as dark a bathroom as possible. Many saw the "light." Triboluminescence occured with the crushing of a number of different items including many minerals. Perhaps ear tones are a manifestation of some unknown or "unseen" occurance in the rocks during the sequence of events leading to the quake event itself.
Lights have been seen before and during some quakes. I saw them on several occassions during the aftershock sequence following the Northridge quake of 1994. Some occured a minute or two before an aftershock and were over the Simi Hills.
Many of the events discussed here were seen before the July 28, 1976 Tangshan earthquake in China. A sudden thought would be if animals really do respond to something before a quake, perhaps they hear a sound to high or low for human ears, or are responding to, an as of yet, unrecognized or recorded phenomena.

Bob Baum, thinking outloud in Woodland Hills.