RESONANCE (5 letters) The term REPEATING SOUND can be solved by two crossword solutions: ECHO (4 letters) and RESONANCE (5 letters). An ECHO is a sound or noise that is reflected off a surface and heard again by the listener. It is usually caused by a single reflection of sound waves, and is heard after a delay of a few milliseconds. RESONANCE is the reinforcement or prolongation of sound by reflection from a surface or by the synchronous vibration of a neighboring object. It is the result of multiple reflections of sound waves, and is heard as a continuous sound.