After ripping ALL the carpet off the floors, and further inspecting what was underneath, we found a few "holes" in the Living Room and Den floors that had plywood fitted over them to cover them up - ugly. It appears that vents came out of these holes at one time and there were probably iron grates that went on top (wish we could find those somewhere). But since the grates are nowhere to be found, and we don't use those vents anymore due to upgraded venting, the holes are not needed.
So, my crafty husband went into a closet in the upstairs guest bedroom and carefully cut out some of the hardwood floor from there (guess we'll have to put down carpet in that closet) and was able to piece together the flooring in the Living Room and Den.
The Hole - where you can peer down into the basement
Joey put plywood down and then cut the hardwood boards
from the closet to fit the hole (my living room is nice and dusty now).
No more holes...