There are three kinds of noise mechanisms which are stick-slip, self-excited vibration and unstable dynamic behavior. This study is of a pad unstable behavior caused by pad spring contact stiffness and weak forces and improving a lower squeal noise due to self-excited vibration in brake system. This paper discusses a theoretical approach, numerical and experimental test to understand the squeal mechanism for unstable pad behavior and the analysis and measurement of mode coupling between brake components to decrease noise propensity. Three different approach are considered to understand noise mechanism. Fundamental approach is more important than experimental modal analysis, CEA (Complex Eigen value Analysis) because the minimal vibration analysis is principle approach which has been proved by many researchers. CEA and modal test is useful to study the relationship between lower squeal noise and self-excited vibration for more details. The case studies to be validated by dyno or vehicle test are introduced in this paper.In conclusion, the general guide lines for stable pad movement will be proposed after analyzing a pad unstable behavior and the practical frequency guide lines of disc in the component-level analysis be suggested to avoid the self-excited vibration in the system-level test during squeal by theoretical, numerical and experimental approach. The frequency guide lines are reviewed by statistical database by conducting historical DOE for various brake systems.