The US Coast Guard says it has to remain "optimistic" as the search for a missing submersible near the wreck of the Titanic continues. Noises detected by sonar raised hopes the five people onboard are still alive, with Captain Jamie Frederick telling reporters "operations were relocated in an attempt to explore the origin of the noises." Carl Hartsfield, from the Woods Hole Oceanographic Institution, adds that the sounds "have been described as banging noises." IMAGES AND SOUNDBITES