The Shepard Tone is a well-known auditory illusion of a musical chord (or sequence of chords) that seems to ascend (or descend) forever. An example of its use is the sound of the Batpod in the Dark Knight / Dark Knight Rises movies by Christopher Nolan. In fact, the film composer Hans Zimmer has used it in the score for several of his collaborations with Nolan.
In the film Dunkirk the Shepard tone illusion was used too, as well as a different auditory illusion. As far as I know this illusion does not have a proper name, though it seems to be associated with Jean-Claude Risset. In Dunkirk they used the sound of a ticking watch, and its tempo seems to slowly increase continually.
Here is a simple illustration of the effect.
Written by Jaap Scherphuis, website a t jaapsch d o t net.