Spot Appeared after drying

I cleaned some carpet came out great. Lady calls me two days later as tells me three spots appeared in three different areas of the house.  Went back to reclean.  The spots are orangish in appearance like a circle.  I re-presprayed and extracted and they where gone. called me back again came back!  The spots were not there orginally so I have no clue could it be something in the pad that got pulled up.  It may be rust the house had lots of rust stains but these spots are pretty big.  The carpet is off white probably 20 years old.  Any suggestions on how to remove.  I only used prespray enzyme and hot water extraction no other soap or chemicals.  Thanks

Try using and emulsifier in your extraction wash then mist on some acid rinse and speed dry with an airmover for 30 mins