Canadian officials are investigating the source of a mysterious pinging or humming sound that appears to be emanating from the sea floor.

Throughout the Fury and Hecla strait, a channel of water in the Nunavut region, a ping sound can be heard that is accompanies with a noticeable decline in sea mammals that is normally rife with seals and whales in the remote area of northern Canada since the summer.

Ashley Lemire, senior communications advisor to the Department of National Defence, issued a statement on behalf of the department explaining the steps that have already been taken regarding the pinging sound:

“The Canadian Armed Forces are aware of allegations of unusual sounds emanating from the seabed in the Fury and Hecla Strait in Nunavut. A CP-140 Aurora aircraft was dispatched on Tuesday, November 1 under the mandate of Operation LIMPID to investigate the alleged sounds,” according to a statement issued by Ashley Lemire, senior communications advisor to Canada’s Department of National Defence.

“The air crew performed various multi-sensor searches in the area, including an acoustic search for 1.5 hours, without detecting any acoustic anomalies. The crew did not detect any surface or subsurface contacts,” she explained. “The crew did observe two pods of whales and six walruses in the area of interest. Operation LIMPID is the routine domestic surveillance of Canadian air, maritime, land, space, and cyber domains as well as presence in Canada’s aerial, maritime and land approaches.”

While a source of the sound is unknown, some theories being named in other media reports include the noise being produced by sonar surveys of local mining companies to make detailed maps of the sea floor in a search for offshore oil and gas. Another theory is that Greenpeace activities is creating the sound on purpose to frighten wildlife away from hunters.