Australian search authorities narrowed the search for the missing jet last month after picking up a series of pings near where analysis of satellite data put the last location of the Boeing 777, some 1,600 km off Australia's northwest coast.
CNN said authorities now almost universally believe the pings did not come from the onboard data or cockpit voice recorders, but instead came from some other man-made source unrelated to the jetliner that disappeared on March 8, according to Michael Dean, the U.S. Navy's deputy director of ocean engineering.
"Our best theory at this point is that (the pings were) likely some sound produced by the ship ... or within the electronics of the Towed Pinger Locator," Dean said.
The discovery of the pings on April 5 and 8 was hailed as a significant breakthrough but no further promising signals were heard before the expiry of the batteries on the black boxes' locator beacons.
A scan of the area around the pings with an unnamed submarine failed to find any sign of wreckage and no debris linked to the plane has ever been picked up despite the most extensive and expensive search effort in aviation history.
Australian authorities leading the search did not immediately respond to requests for comment.
MH370 was carrying 227 passengers and 12 crew when it vanished on March 8. Authorities have not ruled out mechanical problems as a cause but say the evidence, including the loss of communications, suggests it was deliberately diverted thousands of kilometres from its scheduled route from Kuala Lumpur to Beijing.