Hi, have you ever thought of formaldehyde smell. Carpet has this in it. I bought a mobile home and it had the same smell. After 4 years Of shampooing carpet 3 x aweek I tore it out and put wood laminate flooring. Fixed the problem. I also used a sealer on the sub flooring to block any odar that was in it. Not all carpet is that bad. But some is. I hope this helps.