Thumping noise coming from rear passenger

Thumping noise coming from rear passenger I have a 2013 Dodge Grand Caravan, and when I close the sliding doors, a thumping noise starts up in the rear passenger side. I have no clue why it does that, I thought it may be the powered sliding door, but then I unplugged it and the noise still appeared. Does anyone have a clue of what that may be, and how to fix it?