The U.S. Coast Guard announced via Twitter early Wednesday that a Canadian aircraft with sonar capabilities had "detected underwater noises in the search area."

Remotely operated vehicle operations (ROV) were then relocated "in an attempt to explore the origin of the noises," according to the Coast Guard.

"Those ROV searches have yielded negative results but continue," the Coast Guard tweeted.

A former employee of OceanGate alleged in a 2018 counterclaim lawsuit that he was fired for raising concerns about quality control and testing of potential flaws in the same experimental submersible that went missing this week.

David Lochridge, an engineer and submarine pilot, claimed in his counterclaim against OceanGate that he was hired in 2015 by the Everett, Washington, company to ensure the safety of all crew and clients during the submersible and surface operations of the vessel called Titan. But when he expressed concerns about the design and testing of the minisub's hull, he said he was terminated by the company.

OceanGate had initially sued Lochridge alleging, among other things, breach of contract, fraud and misappropriation of trade secrets -- all claims he denied.

In its lawsuit, OceanGate accused Lochridge of breaching his contract by discussing the company's confidential information with the Occupational Health and Safety Administration "when he filed a false report claiming that he was discharged in retaliation for being a whistleblower."

Read more here.

-ABC News' Bill Hutchinson

The U.S. Coast Guard sent out its latest release Tuesday night on the search for the missing submersible at the Titanic crash site.

According to the latest release:

Sunday, June 18, 8 a.m. ET: Submersible launches, supposed to resurface at 3 p.m., but an hour and 45 minutes into the dive, it loses contact.

Sunday, June 18, 5:40 p.m. ET: Coast Guard receives report of overdue submersible.

Monday, June 19: Coast Guard Air Station Elizabeth City, North Carolina, and C-130 Hercules aircraft, as well as a Canadian P8 aircraft equipped with underwater sonar capability, search for the missing submersible, according to a previous release.

Tuesday, June 20, 7 a.m. ET: Bahamian research vessel Deep Energy arrives.

Tuesday, June 20, 4 p.m. ET: C-130 crew from Air National Guard 106th arrives.

-ABC News' Joshua Hoyos

Members of a committee specializing in submersibles expressed "unanimous concern regarding the development" of Titan in a 2018 letter addressed to OceanGate CEO Stockton Rush, who is one of the passengers aboard the missing vessel.

The letter was obtained by The New York Times and was later authenticated by ABC News.

The letter warned of possible "catastrophic" problems with Titan's development that could have "serious consequences for everyone in the industry." The letter goes on to say that OceanGate's safety claims were "misleading to the public" and insisted Titan be reviewed by a third-party organization.

The letter, which was addressed from the Marine Technology Society, was never approved to be sent to OceanGate though was quickly leaked to its CEO, according to committee chair William Kohnen.

"The letter did represent in 2018 the consensus by many people in the industry that they were not considering following the standard safety protocols and designs that the industry uses," Kohnen told ABC News.

Though he wishes it was not leaked at the time, nor now to The New York Times, Kohnen said he stands by the letter and its warnings.

"The company had indicated that their state of innovation was beyond, beyond what was allowable within the regulatory standards we have today and that they would proceed without certification," Kohnen said. "That worried a number of people in the industry."

Kohnen acknowledged that OceanGate did "heed" some of the comments made in the 2018 letter.

-ABC News' Amanda Maile and Victor Ordoñe​z