Squeal noise is observed frequently when one metal counter face slides over another metal counter face under certain conditions. Squeal frequency range is 500 Hz - 20 kHz, with very sharp peaks and high sound pressure level. Two cases that squeal noise is often found are railway systems and braking systems. In this book author proposes new experiment-based method to predict squeal noise occurrence in a structure with friction. It is found that modal coupling instability analysis is an appropriate mechanism to explore more deeply about this kind of noise. There are two aspects that have significant role and related each other in squeal noise generation i.e.; the structure and contact surfaces. The author proposes an idea to predict the squeal noise occurrence by experimental modal analysis and experimental spatial matrix identification. Using spatial matrices that derived from experimental modal data, unstable mode coupling that causes squeal noise can be predicted within the practically realistic range of friction coefficient and contact stiffness.