Bio-duck

Bio-duck is a quacking-like sound which was first reported in the open ocean by submarines in the 1960s. It is recorded frequently around the coasts of Australia, and in particular in the Perth Canyon.
The sounds were originally detected by sonar operators on . They are audible with frequencies from 50 to 300 Hz. The duration of the calls is between 1.6 and 3.1 seconds. The sounds occur many times per day from winter to October, and then taper off until December; they are not heard again until the next summer.
In 2014, it was claimed that the source of the sound had been identified as being vocalisations from the Antarctic minke whale. Although the reason for the vocalisations remains a mystery, they appear to be produced near the surface before deep-feeding dives. There are hopes that analysing the history, location, and frequency of the sounds will enable cetacean researchers to learn more about the life cycle of the minke.