Underwater noises have been detected in the area of the search for a sub that went missing while carrying five people to the wreckage of the Titanic, the U.S. Coast Guard says.

In a tweet on Wednesday, the Coast Guard said the noises were picked up by Canadian P-3 aircraft, and as a result, underwater operations were relocated to try to locate the origin of the noises.

Those operations haven’t turned up any findings yet but the underwater operations are continuing, the Coast Guard said, adding, “The data from the P-3 aircraft has been shared with our U.S. Navy experts for further analysis which will be considered in future search plans.”

Rear Admiral John Mauger of the Coast Guard also said that the site is “incredibly complex,” and that there are metal objects in the water and around the site. He said naval experts are being used to help classify or provide better information about the source of the noise.

Mauger said officials will hold onto hope for the sub-passengers “as long as there are opportunities for survival.”

“Over the course of the next 24 hours, we are going to bring additional vessels, additional remote operated vehicles, and we are going to continue to fly in the air. So, we’ll continue to look,” he said.

Pakistani businessman Shahzada Dawood; his son Suleman; Hamish Harding, the British tycoon; and French explorer Paul-Henri Nargeolet were on the sub, along with Stockton Rush, the CEO of OceanGate Expeditions, the U.S.-based company that planned the voyage.

Since the sub went missing, the U.S. and Canadian coast guards and the U.S. Navy and Air National Guard have reportedly combed a combined area of about 7,600 square miles, which is larger than the state of Connecticut.