There is no carpet in the passageway. The noise occurs as a direct result of walking on the floor board, nothing else. The (teak/holly laminate?) board is one piece over the entire passageway floor, and I could not see any simple method to lift it to look underneath. I cannot slide a piece of paper between the floor board and the wall panelling on each side.
The noise seems to be a result of the floor board moving vertically when stood on, and it rubs on the vertical panel in front of the battery compartment. Classic creaky floor - haunted house style!
I don't know how that board is fixed down (no visible fixings), but I suspect it is a little warped.for some reason, and the high point sags when stood upon.