EMI (Electromagnetic Interference) is one of the major concerns today in the automotive industry. The main reason is that vehicles are using and depending more on electronic technology. The causes of electromagnetic interference problems are not only related to the ever-increasing number of embedded electronics systems in vehicles, but also to external electronic devices that are brought in to automobiles by drivers and passengers (e.g. cell phone, MP3 players, Bluetooth devices, portable video games). Even though these problems can cause serious issues on safety systems like the airbag, their symptoms are often noticed in a less harm way in the sound system. A very common EMI problem in automotive sound systems is a particular noise caused by devices that uses GSM (Global System for Mobile Communications) technology. Most of the cell phones and vehicle locators rely on GSM technology. In Brazil there is a national normative known as Contran 245, which when issued, will enforce the use of locators on all vehicles commercialized in Brazil. Hence, EMI problems caused by GSM technology will likely to be noticed more often in Brazil.GSM devices emit short duration RF (Radio Frequency) pulses at a rate of 217Hz. The interference pulses contain the fundamental frequency plus a large number of harmonics that overlaps the frequency range of listening, which goes up to 20kHz. This work presents a detailed study of the EMI of GSM devices in automotive sound systems using state of the art numerical simulation technology provided by ANSYS HFSS and ANSYS Designer tools. A system model comprising a vehicle with a complete sound system, wiring harness and GSM devices communicating to a base station GSM tower is used for this analysis. Measurement data is also presented showing a good match to the simulated results. Options to decrease the GSM interference and overcome this issue are also discussed.