I'm with Henry that it is unusual to put plywood on top of hardwood floors before laying carpet. I'd be thinking there is some severe damage to the floor. Your email address mentions bayou.com. If you are around a bayou, then I suspect some sort of severe moisture/flood problem comes to mind along with mold and mildew. Look up under the floor joists for any apparent damage. I was going to suggest pulling up the carpet and plywood in a closet but your main damage is probably out in the middle somewhere. Look under a cabinet also.
It doesn't sound hopeful. Post back with what your inspection of the floor joist area shows.