OK, I had pretty much the same thing going on with my bedroom slide and what it turned out to be was dry rot, water had gotten into the core of the floor of the slide and it just rotted, what is happening is the rotten wood is giving way as the slide goes in and out and is breaking down to the point it is now created a crack in the outside skin, I had to take out the mattress and expose the guts of the slide mechanism and that's when I saw the dry rot. Had to have the slide pulled out and new floor installed. Good luck.