In 1997, Bloop was detected by U.S. Navy "spy" sensors 3,000 miles apart that had been put there to detect the movement of Soviet submarines, the magazine reports.
The frequency of the sound meant it had to be much louder than any recognised animal noise, including that produced by the largest whales.
I think it is awesome that there could be some form of animals that have yet to be discovered, I remember hearing that we know more about Space than we do about our own oceans. I find that amazing to say the least. To imagine something bigger than a blue whale in the extreme depths is scary as well as fascinating. I wonder what scientists think when they go in small craft to deeper parts of the ocean.
Also there are five other mysterious sounds which NOAA cannot explain and remain baffled by them. Page where you can listen to them.
http://archives.cnn.com/2002/TECH/science/06/13/bloop/
http://en.wikipedia.org/wiki/Bloop