There is no carpet in the passageway, it is a single board of teak/holly laminate flooring.
The creaking happens when walking on the floor board. The board is slightly warped and moves (almost invisibly) as you walk on it, rubbing against the wall panel on the side of the battery compartment.
ps this is the third time I've tried to "reply" using the group web interface. My replies just seem to disappear into the ether.