Suspect juvenile Blue-winged Teal. Whiten the chest a bit on the bird illustrated by Sibley, and it comes pretty close. I did not realized until looking in his book this morning that the youngest Blue-wings lack the white spot at the base of the bill. I also did not know until reading his note, that juveniles of both Blue-winged and Cinnamon often bleach to pale straw colored from September to November. Seems consistent with what I saw. It still could prove out to be something else, but that is my best guess at this point.