There's something in my house or in my walls that was not invited in.

It sounds larger than a mouse, but size is difficult to judge on sound alone.  I've heard what I think are chirps, but that means little.  Yes, birds chirp, but so do squirrels.

It moves with speed.  It is not afraid to make sound during daylight hours.  It will quiet down if I try to locate it, but unless it hears me moving it seems to have no qualms about being loud.

I have yet to see it.  Sometimes I'm convinced it's in my house, using furnature for cover to avoid detection.  Sometimes I think it's in the walls.

Once birds nested in a hole in our porch.  Then one year they didn't come back.  Then squirrels built a nest.  After failed attempts to drive them out I gave up, and resigned myself to squirrels living there.  But they seemed to have abandoned it too.

Now, suddenly this new noise.

If it is inside the house, how did it get in?  If it is in the walls then I actually have a pretty good idea.  when adding insulation we meant to cut off decorative thing on the porch from "Entire rest of the area above the ceiling."  We never did get to it, and it needs to be done from the inside because then we can scare anything inside outside before said sealing off, otherwise we risk trapping something inside the above the ceiling space.

This never getting to it is why this post from 2012 was interrupted by a squirrel above the ceiling and the subsequent discussion of the etymology of the word squirrel.

The walls in my house are inadequately insulated.  At least I think so.  I don't know that much about walls so I could be wrong on that point.

Inadequate insulation means space to move.  It is conceivable that something that made it into the space above the ceiling could transit to the walls and from there have mobility around the room I've been hearing an animal in without ever actually being inside of the room.

I do not know.

I just know that there's something moving around in here, I never see it, and it isn't myself, the cat, or the gecko.