I drive a 94 cobra that sometimes makes a weird noise when I have the radio turned on. I currently have an aftermarket radio installed, but the car made the same noise with the factory radio. It doesn't do it all the time, but occasionally when I turn the car on I hear a rather loud buzzing noise over the speakers, whether I'm playing any music or not. The noise is not dependent upon the volume of the radio either. The buzz changes in tune with the RPM's of the engine as well as other things like the movement of the wipers, turning on or off the lights, or turning on or off the heat/ac. I really have no idea what causes it, because it does not happen all the time. Thanks!