Underwater noise or explosions caused healthy beaked whales to beach themselves in the Bahamas in March just as the Navy was conducting underwater tests in the area, according to a report released yesterday by the National Oceanic and Atmospheric Administration. The report does not say outright that the Navy sonar tests or explosions caused the deaths, but its findings raise a “red flag” and are “reason for concern,” said Darlene Ketten, an auditory specialist at the Woods Hole Oceanographic Institution who helped conduct necropsies on six of the whales. The Navy has been experimenting with sonar systems that emit loud blasts of noise underwater, and in the past has denied that the systems can disorient and kill whales and other sea mammals, despite environmentalists’ arguments to the contrary.