Televised ducts under slab floor. Ducts are pvc ducts with metal fittings that are very rusted. There is one location near kitchen and living room where there is a double turn making an elevation change where the stone is coming in from outside the pipe. Will attempt to clean and repair but that area may need to be excavated if it cannot be cleared and patched. After that the metal should be spin cast then the entire system spray lined with Duct Atmor duct lining material.