When I have come across the “do it yourself” people, it is usually residue left over from some products they used with the rug doctor or she pulled up some stuff embedded in the padding. What I usually do: Flush the grey spots with hot water, extract and do regualr clean. You get soak with solution, the flush with hot water, then extract then do regular clean. Whatever floats you boat dude. That’s what has worked for me. Hope all is well. You can do it.
Mike Nowlin