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If its the "marbles in a can sound" its normal and described in the owners manual. Mine does it too.
Classic throw out bearing noise. There is also noise when turning the car off, unless you depress the clutch and then it goes away. This is one of the ways GM maintains their uniqueness so their products aren't confused with the Japs or the Germans, who seem to be able to eliminate it. Fifty grand and marbles in a can...