Subaru Whining Noise Over Radio, Ray was almost right

After years of installing high power car audio systems, I have run into several new and used cars that produce a similar whining noise. The noise originates from the alternator and enters the car audio system at the amplifier inputs, not from the radio. The noise is not Radio Frequency, it is in the audio range similar to the 60 cycle hum from florescent light fixtures.

There are several inexpensive alternator noise filters available on the market that are placed on the radio or amplifier.

It can be heard even when the radio or CD player is not running since the amplifier is still running idle.

In some cases a bad diode in the alternator can cause this excessive noise condition. Easiest thing to do is swap it out with a new/rebuilt one. If the noise persists, then I would look into a filter. In some instances you may also find that the radio or amplifier is not properly grounded. In the old days, the best cure was to run a piece of RG-8 copper coaxial cable straight to the battery, connecting the shield to the Negative post t and the center to the Positive. Run this all the way to the radio and connect it’s power lead(s) to that. This will shield/isolate it from noise generated in the engine area.