Appreciate the continued input, but have settled my mind that it was a Hercules with extra fuel nacelles, hopefully on its way to some sort of covert op against Wisconsin or Minnesota. Definitely a prop sound, JP Jones, which is why I ran out to look at it in the first place.
It was definitely not a Gigant, or some Blohm and Voss variant, Wicky, though I like that picture. Now, there was a time about 10 years ago when I was still living in Chicago when I was walking down the street and heard a distinctive propeller sound, and looked overhead to see a Ju 52. I was so taken that I walked into the middle of Clark Street and nearly got hit by a car, which I figure would have made me the last WW2 Luftwaffe-caused casualty.