Marine scientists encountered a previously unknown population of Blue Whales in the Indian ocean last year.

NYT:

[url=https://www.nytimes.com/2020/12/23/science/blue-whales-indian-ocean.html?smid=url-share]A New Population of Blue Whales Was Discovered Hiding in the Indian Ocean - The whales in the group seem to sing a unique song.

The NYT article is the only instance on the web I've found that included an audio recording. If you can't access it, I believe this to be a faithful approximation...

<ATTACHMENT filename="bluewhalesong.png" index="0">[attachment=0]bluewhalesong.png</ATTACHMENT>