> The voltage produced by an alternator in a running car will have about
> 10-15mV of DC ripple on it. Battery voltage is quite flat.

        Unfortunately I don't think that's as simple a solution as it sounds since
other devices can generate noise. For example, I regularly have an inverter
pluged in to charge batteries while the car isn't running, that inverter
surely inserts an amount of noise into the cars electrical system (I can
hear it from the radio). TTYL

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