Abstract: Ball socket is injected on metal link in link assembly of wiper system, which is an important component to transmit force. Aiming to abnormal noise issue from wiper system during the trial production for a certain vehicle, based on quality control method, confirm every terminal factor one by one, two direct causes were identified: the clearance between the ball socket and metal link, and unqualified the dimension of stamped step. With 5why tool, deeply analyze the root causes:poor injection process parameters and lacking of control for dimension in supplier side, and develop improvement strategies to eliminate abnormal noise, which provides a reference of abnormal noise issue for similar mechanical structure.