Brake noise causes discomfort to passengers and a perception of reduced vehicle quality. Other types of vehicle noises have been significantly reduced and consequently brake noise and vibration are becoming more perceivable by owners, leading to high warranty costs. It is known in the Brake Industry that the natural frequencies of brake rotors may have a significant participation in disc brake squeal generation, and, a robust process control of this characteristic in the manufacturing gives an important contribution to reduce brake noise. However, recent studies have demonstrated a significant variation of natural frequencies due to manufacturing and this is the outcome of carbon equivalent content in gray cast iron. This paper is concerned with the understanding of this phenomenon and its influence on disc brake noise generation. For this research, it was manufactured two batches of this rotor from two different grades of carbon equivalent. The influence of carbon equivalent on natural frequency variation is analyzed through an Experimental Modal Analysis (EMA), and, at the end, the brake noise generation is evaluated using a dynamometer test. The results show a different brake noise behavior between the two rotors’ batches and indicate that the natural frequency is significantly influenced by the content of carbon equivalent present in gray cast iron brake rotors.