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sounds like it might be as simple as a leaf or twig has gotten in through the air ducts & vibrating on the a/c heater fan happens to me all the time depends were you park the car.

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โˆ™ 2005-03-16 14:06:01
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Q: What causes a whirring sound only when the heater or AC is on - sounds like it is revving up and doesn't go away until you shut the heater or AC off?
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