There was some Discovery show where they were using the old sound recording systems for submarines to research whale migration, etc. The expert was playing various recordings and saying things like “that’s a Blue Whale off the coast of Nova Scotia, that’s a Gray Whale about 200 miles west of San Diego.....and this one (plays a sound that is almost electrical/ synthetic) - we have no idea! It’s in the Indian Ocean trench at about 1000’” (I’m pretty sure it was around India somewhere, and it was real deep - guessing on the depth). Pretty weird.