Found a broken piece of plastic on the floor in front of the fridge. No idea what it was, but as it was the same color white as the fridge internals, I saved it. Next day noticed the left door was not closing properly. The bottom hinge on the left door's flapper was the source of the plastic debris. The hinge just clips on the door, but the part had broken. The video on the Appliance Parts Pros page for the part was invaluable! Taking the flapper off and replacing the hinge was a snap - maybe 5 minutes total.