Intermittent groaning sound when accelerating
This 2007 Chevrolet Impala with a 3.9L engine, makes an intermittent groaning sound when accelerating. The dealer finally had the regional GM engineer ride with him. He says that this occurs when the car shifts from 3 to 6 cylinders (a fuel saving measure) and nothing can be done about it. Other than that, this is a wonderful car.
Sounds like he is telling you the truth. It could just be the switchover from 3-6 cylinders. I would give it time and see if it becomes less noticeable.
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