D. This is a contemporary issue due to global warming, etc
In 1832, as the Beagle was exploring the Bahia Blanca along the coast of Argentina, Darwin discovered the bones of fossil mammals at two localities. In a place where armadillosabounded, he was especially struck by what looked liked the outer shell of an extinct form of armadillo.
Personally I don't hear any but lots of my friends say they do. I obviously just hear silence but if you hear a ringing when there not plugged then I'd visit a doctor :D
