While the factory plywood floor was up, why not? Does it help? I'd have to do before-and-after experiments to see, but that seemed way too much like work. That is, I'd have to do (1) noise measurements as bought, (2) add insulation only (as Hein recommends), then do noise measurements, and (3) take floor out again, and insulation as well, add Noico, put insulation and floor back, then do more noise measurements. I'm not that dedicated to the pursuit of knowledge.
At this point, I'm now installing Thinsulate in the walls. I'm adding leftover Noico in spots because I have it. Its effect is probably marginal, but the Noico is already paid for.
Oh, and our trip to Utah was great. Attached is an image of The Citadel in Bears Ears. It is on a peninsula of rock jutting 300 yards out into a canyon -- apparently a fortified place 800 years ago. More info is at
http://www.girlonahike.com/2018/12/hiking-to-citadel-ruins-cedar-mesa.html
