Might want to check the plastic parts of the seat where the hinges are. I know that I had something similar that sounded like it was coming from the door behind me (driver) and it was the plastic covers over the rear seat hinges that were rubbing together. I put a piece of foam in between the two pieces, problem solved.
2012 1500 Laramie CC 4x4/Hemi/Deep Cherry Red Crystal, Bright Silver Metallic
MODS: Volant CAI, 20% Tint All Around, Diablo Trinity w/Hemifever, Magnaflow Cat-Back, Daystar 2.5" Lift, BP Catch-Can, LuVerne 3" Polished SS Tube Steps, Magnaflow Y-Pipe, Fuel Throttle Chrome 20x9 +1 with Nitto Terra Grapplers 295/60R20, 85mm Ported Throttle Body