Strange sound phenomenon - DAT ATR-42 | Landing & Takeoff - Stord airport, February 2024 

When you make noise, sound waves travel away from you in every direction, making an expanding sphere. Since the air just above an open body of water is cooler than the air slightly higher up, the speed of sound is slightly lower above the water’s surface. The temperature gradient above the water translates into a gradient in how fast sound travels; sound waves further from the water will be faster than those below them. The difference in speed causes the expanding sphere of sound to change shape, flattening into a wall or even focusing the sound downwards. That’s why sound travels further over water: less is lost up into the air, meaning more of it ends up in your ears - or your neighbors. Those props are driven by jet turbines so that sound is amplified more coming over a body of water. Notice the sound changed back when it got over land. I've spent a lot of time in boats fishing and things do sound strange over water and the mountains may create a slight echo as well.