Hello, thank you very much everybody for the recommendations!!!
I always use the Audio Technica cleaning solution for stylus and a gel pad, so I think is more than a dirty stylus.
I decided to try a new cartridge/stylus. I ordered the Ortophon 2M Blue before reading your suggestion Elliot.
Problem solved!! Now my system sounds good again, a little different because of the 2M Blue.
Thanks again for your commenters!!!