There are multiple causes for the engine noise through the speakers. first is the Ignition Wires and / or Spark Plugs. Next is your radio antenna, radio ground. Next are the noise supression grounds. STRAP-ENGINE TO SHOCK, STRAP-EXHAUST TO BODY, STRAP-HOOD TO BODY, STRAP LOWER HINGE TO LATCH. STRAP-UPPER HINGE TO DECKLID All of these play apart in providing quality sound.