I do have a theory, actually. According the the documents the others found, the Strangerground is an artificially created reality plane. Whereas the Realground and the Underground seem to take shape naturally thorough the various worlds.

They may not have the power or resources to duplicate the feat on a broad spread. Which means when they return us to our own worlds, we would only have access to the Realground, where these noise do not seem to appear until it's too late, and the Underground....which only the dead can typically access.

[Kurama is picking at his own food, more out of necessity than anything. His tone is quiet and calmly thoughtful.]