Friction between two relatively sliding surfaces in mechanical structures possibly excites unstable vibration, which emits squeal noise. In this paper, the authors propose an idea to predict the possibility of squeal noise occurrence in actual structures having relative sliding surfaces with friction by means of 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. By this method it is possible to calculate the possibility of squeal noise incident and its frequency within the practical realistic range of friction coefficient and contact stiffness. The method is presented with showing an experimental verification study using a simple L shape frame.