04-Sububan help with noise

     Have a 2004 Suburban 42K - 4WD - with auto temp rear heat/air control. With all rear heat and air controls off, there is a noise coming from
the lower passenger side panel, near the rear door, seat forward to enter the 3rd row seating, there is a 4"X4" fined panel near the floor, sounds like a motor trying to adjust its self. I turned on the rear fan, it works and is all the way to the rear of that same panel, near the tailgate. I'm not sure if this is normal because this is a new purchase. Could it be a heat/air door trying to open or close that is not completing the cycle.
Are there any other problem areas that I should check out. I know that on our 99 Blazer 4X4 the lower ball joints had never been greased because the fittings were on top and kind of hidden. Are there things like this that I should check out right away. Thanks

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