One thing that is sure to disturb a car audiophile is speaker problems. The audio system sounds beautiful, then, all of a sudden, there is a buzz coming from one of the speakers or no sound at all.
Usually you can do the troubleshooting and fixing yourself.
If there is a buzz coming from a speaker, then the voice coil or dust cap may be loose. The buzzing is generated from between the cone and a glue joint, and it is happening because there has been thermal damage to the speaker. Such a problem is due to too much power getting to the speaker from the amplifier or you simply turned the volume up too high. To ascertain if that is indeed the problem, expose the speaker and gently press a fingertip into its dust cap as your sound system is playing. The dust cap is the piece that sits in the center of the speaker. Keep the finger tip on the dust cap as the cone comes back to its return position. If the voice coil or the dust cap is loose, you will feel the voice coil dragging.
If you cannot isolate which speaker is having the noise problem then disconnect one speaker at a time until the noise stops.
It is possible that noise can be coming from a speaker but it is not at fault. If this is the case, then a component of the audio system is not properly grounded. To isolate which component is causing the problem, simply disconnect the RCA cable connection between components one at a time until the noise stops. The component that was disconnected immediately before the noise stopped is the culprit. In this case, properly ground the component and plug it back into the system.
A bad installation can also cause noise from a speaker. It is imperative that the RCA cables carrying the audio signal through the system are not routed too close to an electrical source or microprocessor. If the cable is too close, then the noise generated from the electrical source transfers onto the cable and is played by the speakers. Simply re-route the audio cable and be certain that it is not near any electrical sources.
Finally, if there is no sound coming from the speaker, then it is possible that the tinsel lead coming from the speaker connection terminal to the speaker cone has broken due to fatigue. You can determine this is the case by touching a voltmeter to the speaker to see if there is continuous voltage going through. If there is not, then you have just confirmed the broken speaker connection.