Sound notification on specific contacts in my messages app.

There is no sound to notify me if I get a message from several contacts on my list. I also see a "no sound" icon by their names on my list of recent texts. I have turned on sound notification for messages on everything I can find and have gone into the "info" section for these contacts but can see nothing I can change to fix it. I'm sure someone out there knows the answer to this and can enlighten me!