US Navy Photo
The sound is reported to be coming from the same area where search crews detected sounds consistent with an aircraft's black box.
The Australian navy has been dropping buoys from planes in a pattern near where the Ocean Shield's signals were heard.
Royal Australian Navy Commodore Peter Leavy said each buoy is dangling a hydrophone listening device about 300 meters (1,000 feet) below the surface. The hope, he said, is that the buoys will help better pinpoint the signals, along with the Ocean Shield, which is slowly dragging a U.S. navy pinger locator through the water.
The acoustic data will require further analysis, but if confirmed, would be the fifth underwater signal detected in the hunt for Flight 370, which disappeared on March 8 en route from Kuala Lumpur, Malaysia, to Beijing.
239 people were aboard.