Rear blend door actuator was the problem. Easy fix, but taking off the trim panels was a hassle. There was also an issue finding the correct non-OE replacement, as there are two actuators right next to each other in the back assembly. My local AutoZone stocks both, so was easy to find.
The correct non-OE replacement parts are:
Dormant 409-202 (the actuator closest to the back)
Dormant 409-213 (the actuator closest to the front)
Here is the correct order of disassembly:
To make the job easier lay all your rear seats down flat. Now remove three scuff panels: rear hatch top, rear hatch bottom, back seat floor. All three have the same locking push tabs. Just pull straight up to remove. Now open the rear hatch storage bay (where the vehicle jack is). Remove the four hex bolts that hold this on. Now remove the two trim panels covering the back and middle columns. They pull out straight. You don't need to remove the seatbelt bolts at the top if you don't want. These panels can just hang and be moved to the side of they get in your way. You will, however, need to unbolt the bottom seatbelt bolt on the second row, as this bolt holds down the main trim panel you're trying to remove. To unbolt, put your second row seat in cargo mode by pulling the red fabric pull lever and tipping the seat forward. Now you can access the bottom seatbelt bolt. Remove with a Torx 45 bit. Next, you will need to remove the rear driver side cupholder trim piece. Using a flathead screwdriver carefully pop up the round push fastener in the middle of the tray. Pull up gently, so you don't damage it. Now unbolt the hex bolt holding the cupholder trim piece to the floor. You should now have complete access to the main trim panel covering the rear HVAC assembly. Work your way around the trim piece, popping it straight out as you go. When you can almost freely get it off, reach in and disconnect the wiring harness to the door lock. The whole panel should now come off. The two rear actuators are between the HVAC assembly and the outer frame, and are nearly impossible to get to. To reach the two actuators themselves you will need to unscrew two bolts holding on the HVAC assembly. There is a locking nut near the front. Find it and remove. There is a hex bolt near the middle of the assembly. Find it and remove it now. These bolts are on the side face of the HVAC assembly and screw into the side frame. Now slide up the plastic air duct on the second row column where it connects to the main HVAC assembly. You should now be able to pull the front of the assembly away from the metal frame enough to be able to get to the actuators. Start your vehicle and set your temp gauge/blower setting until you hear the noise of the failing actuator (grinding, clicking, etc). With the car still running go back to the rear HVAC assembly. Disconnect the wiring harness to one of the actuators. If the noise stops, this is your problem actuator. If not, unplug the other one. If the noise stops, this is the problem one. Remove the actuator by removing three hex bolts that mount it to the inside of the HVAC assembly. Two at the top and one on the bottom. Remove the actuator and replace with the new one. When you install the new actuator, you may need to turn the insert hole on the HVAC assembly to get the new part to pop in, as it only goes in one way. This makes sense if you look at what you're doing. Assembly is the opposite of disassembly.
Hope this helps! I'm very happy to not be bothered by the noise any more. And the replacement part was only $40. You guys are the best! New user, but I'll be hanging out more now.
