The following is a list of sounds, the sources of which remain unknown:
This list is incomplete; you can help by expanding it
The following unidentified sounds were detected by the USA National Oceanic and Atmospheric Administration using its Equatorial Pacific Ocean autonomous hydrophone array.
- Upsweep ('Upsweep' may have been tracked to an undersea South Pacific mountain that was not previously identified as a "live" volcano, although this is still unconfirmed.)
- Whistle ('Whistle' was only detected by a single autonomous hydrophone from the array.)
- Bloop The NOAA identified the sound as "consistent with icequakes generated by large icebergs as they crack and fracture".
- Julia The NOAA reports that "The most likely source of the sound formerly known as “Julia” is a large iceberg that has run aground off Antarctica."
- Slow Down The NOAA reported that "it is highly probable that this sound was produced by a large iceberg as it became grounded."
- Train The NOAA wrote that the sound "was most likely generated by a very large iceberg grounded in the Ross Sea, near Cape Adare." 
- Colossi of Memnon The sound was probably caused by rising temperatures and the evaporation of dew inside the porous rock of the statue.
- Bio-duck Most likely a sound produced by a great whale such as the minke whale.