This papers deals with the strong dynamic effects (called silo music) appearing during confined granular flow in the cylindrical silos. Silo experiments with dry cohesionless sand during gravitational outflow were performed in a cylindrical perspex model silo. During tests the wall accelerations and acoustic signals were recorded and the mode shapes of the silo structure were determined. In addition, experiments were performed with additional modifications of the silo structure and silo flow. A novel simple mechanism of the origin of silo music was proposed. (c) 2007 Elsevier B.V. All rights reserved.