As with noises found in the radios in your DX shack, the same sorts of principles apply to noise heard in your car or truck radio. The first step is to determine what kind of noise is present, which is done by answering many of the same questions we looked at before. Is it constant or intermittent? If it's intermittent, does it seem to have a regular pattern or is it random? Does the noise affect only a portion of the band? Is the noise present only at night, or at twilight? But with a vehicle radio, we also need to know whether the noise is present when the vehicle is moving, stopped or both, as well as whether it is present when the engine is on or off.
If the noise is always present, even with the vehicle stationary and the engine off, then the source is either external or generated within the receiver itself. Generally, the latter is less likely, although not impossible. If the noise starts immediately after turning the key, but before starting the engine, the cause is likely somewhere in the electrical system, and often it's related to either electronic ignition or some sort of on-board computerized circuitry. If the noise starts when the engine does, then something which is activated by the engine is causing it.
In these cases, you can either choose to live with the problem, get a different vehicle, or consult with an authorized dealer or specialty vehicle electronics expert.
Fortunately, the most common sources of vehicle radio noise are more obvious and easier to remedy. A static-like noise which is present only when the vehicle is moving, and which seems to be more of a problem at higher speed may be the result of a loose, improperly grounded or improperly mounted whip antenna. Check to make sure that the plastic insulator that separates the base of the antenna from the vehicle's body is present and intact. Make certain that the whip's mounting hardware is tight. Check the antenna cable, particularly where it connects to the antenna, and where it makes any significant bends or goes through any tight spaces to see if the ground braid is broken or damaged. In many cases, it is often easier to replace the entire cable unless it has been routed within body sections, in which case you may need to engage a specialist to replace it.
Another common cause of a static-like noise observed only while in motion is static electricity. This often results from the installation of new tires, and may persist for several thousand miles. One option to try to eliminate it is to rotate the tires, which occasionally works. In other cases, static electricity noise can be reduced or removed by means of replacement or added grounding of the receiver.
One additional note on this problem is that with the increase in the amount of fiberglass and other plastics used in the vehicle manufacturing process today, it is often more difficult to establish and maintain a good vehicle ground system. This also applies to the actual mounting of the radio itself, as the metal radio case must be physically grounded to the vehicle frame.
Often, it can be difficult to determine whether the noise is static electricity or a poor ground. One sure way to tell is to drive across an uneven surface. Static electricity noise will be interrupted by the bumps, whereas a ground problem will be enhanced by and timed with the bumps.
A noise which sounds like a combination of popping noises and static may be arising from the vehicle's sparkplugs. If the engine hasn't been tuned up I some time and/or if the sparkplugs are more than the recommended number of miles old, a full tune-up may solve the problem. In more stubborn cases, it may be useful to investigate noise-suppressing plugs, although many newer vehicles cannot accept them - check with your owner's manual or the dealer on this. A whining noise which varies with the engine revolutions is ignition noise, which is usually found in older vehicles.
If all else fails, there are various filters available which can be installed in line between the antenna and the radio and also in the power line just before the radio. If the noise seems to be electrical in nature and generated by the engine or electrical system, the latter should be your first choice, while in the case of static electricity or other noise not being transmitted via the radio's power line, the former may be the better choice.
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