Does the floor feel solid and flat in that spot or is it starting to sag? I think your floor is just like mine in my 335, its made up of 3/8" plywood top, 1/8" or 3/16" Luan on the underside, Styrofoam,and stiffened up with an aluminum frame in-between. I don't think the floor is all that strong or durable, I'm just thinking maybe the floor is starting to sag in that spot and the screws are not and there working there way through the top layer of plywood? I would pull the cover off the belly and see what the screws are holding, but i would guess that some are floor to frame fasteners. That is problem that can't be ignored so I would call Prim time and your dealer to see if they can help, your out of warrantee and it is 2 years old so just prepare yourself to be on your own with this
. I have never liked the floor in my unit and I do believe it will be a problem in the future.