The Bloop sound was repeatedly recorded during the summer of 1997 on the Equatorial Pacific Ocean autonomous hydrophone array over an area of 5000 km. The sound rises rapidly in frequency over about one minute and was of sufficient amplitude to be heard on multiple sensors, at a range of over 5,000 km. It yields a general location near 50 Deg S; 100 Deg W (far off the west coast of southern South America). The origin of the sound is unknown but too loud to be any know biological or living source.
There are a series of unknown sounds that have been recorded in the oceans including: Julia, Train, Slowdown, Whistle and Upsweep. Here is an excellent NOAA site where you can read about some of them.
As usual youtube has them also.