When a wideband sound beam is incident onto a periodically corrugated surface, a series of diffraction related phenomena can occur. In this work, we report the observation of a secondary diffraction, which is different from those previously investigated. The search of the physical origin of this newly observed diffraction leads to the discovery of the possibility of generating Scholte–Stoneley waves, inspired by Guo, Margetan, and Thompson's work in sound backscattering from rough surfaces, through a nonconventional energy conversion mechanism: direct coupling of the incident energy with the periodic interface. This mechanism allows for the Scholte–Stoneley wave generation at any angle of incidence, which distinguishes it from the well-known energy conversion mechanism of the diffraction-related phenomena such as acoustic Wood anomaly and backward displacement in which wave generation is highly angle dependent. The findings of this work not only enrich the understanding of the interaction of sound with periodically corrugated structures but also provide a new surface wave generation method for the potential applications in nondestructive evaluation of materials.