In this work, an experimental and numerical study is performed to understand squeal generation and suppression of a pad-on-disk friction system. Several friction material specimens having various orientation degrees of grooves cut on their surfaces are tested. Numerical studies using the methods of complex eigenvalue analysis and dynamic transient analysis are conducted to simulate the experimental process with the finite element (FE) software ABAQUS. Both experimental and numerical results show that surface modifications of friction material specimens have a significant influence on the squeal instability: cutting a 45 deg or 90 deg groove on the material surface can significantly reduce squeal noise, cutting a 135 deg groove just reduces squeal noise moderately and cutting a 0 deg groove cannot reduce squeal noise. Moreover, the contact pressure distributions for the original surface and modified surfaces are studied to provide a physical explanation of the noise phenomenon. The major finding that friction-induced noise can be reduced by means of suitable structural modifications of the contact interface is expected to have important and much wider applications.