The obvious cure was to access the area via the seat board which was fastened into place with 27 screws. So, I removed the screws and cut the board to make a swing up cover. Maybe it took 27 screws to eliminate rattles but it seemed excessive as I extracted each with a manual screw driver.
After cutting, I filed the edges and corners down on the brass hinges (they had sharp corners that could have cut through the bedding used on the settee), and set them in place. Then I added a finger hole to lift the board.
The unfinished finish work, is to add a brass hook and eye to hold the board up for easy access to the storage area and some padding around the finger hole.