My car does that too until I rev it a little. I thought it was normal. Did you notice it happening before your pulled the instrument cluster? If you are talking about the flap for the center vents or the one for the defrost, Ifind it easier to get to it from the glove box, but if you have the cluster out, it should be just as accessible.

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2001 Dodge Ram 2500 Cummins Turbo Diesel - 4x4, auto, 3.54 gears, long bed
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