There is a Canadian National Park on the border between Saskatchewan and Montana. It is called Grasslands National Park.
★★★★★ · National park
www.google.ca
One of its claims is that, once you get away from the visitor center, you can hear no man made sound. There are no nearby railroads and the flight paths do not cross over it much, if at all. My daughter camped there and said that is is eerily quiet. Spectacular night skys as well. I myself, have not visited it but I have ridden the roads nearby in both SK and MT and can attest to the fact that it truly "in the middle of nowhere".
Here is an interesting article.
Is there anywhere left utterly free of man-made sound? In the first of a series for BBC Future called Last Place on Earth, Rachel Nuwer sets out to find havens where silence still rules – but discovers that avoiding civilisation’s clatter is harder than it seems. In fact, there’s one human noise...
vestibular.org