Summer song of Toadfish

Residents of the Monterey Bay, California area have called the hum keeping them up at night "odd" and "disturbing," but until now had no idea what it was.

According to the Monterey Bay Aquarium, the low humming is, in fact, the mating call of the plainfin midshipman, or toadfish.

The toadfish mates from May to September and produces the humming sound to attract passing females by pressing its muscles against its bladder, at about 6,000 times a minute. The hum can last for up to an hour at a time.