You've heard the sound many times -it appears to rise, and rise, and rise in tone, but it never reaches a climax, or else it takes way longer than you think it should to reach a climax. This is called the Shepard tone.
This video from Vox explains how the Shepard tone works, and why it's so effective in creating tension in a movie, like the Hans Zimmer soundtrack for the new Christopher Nolan historical film Dunkirk. -via TYWKIWDBI