I have no knowledge of dog's knees but I can tell you from a personal side.. If they are doing the cracking noise now then YES I would start doing Cosequin just to be on the safe side. Even if it is nothing now it is not going to hurt and it will prevent for the future.
__________________ Alisha mommy to Guinness Stout 7 & Stella Artois 5 & Teagan 4    Guinness & Stella proud Teapot Club Members |