The West Seattle Hum is a mysterious sound that occurs primarily at night and is loud enough to awaken residents in certain neighborhoods of Seattle.
Listen to the hum (starts at about 20 seconds in).
Articles about the West Seattle Hum:
Ship-unloading operation CalPortland, probable source of the hum, takes action. - from West Seattle Blog.
For a second people were all like, dude, maybe it's a fish, but that was incorrect. - from King5.
Serious research went into disproving the humming fish theory. - from West Seattle Blog.
CalPortland has installed two silencers as an attempt to reduce the hum. - from West Seattle Blog.