Is Noodle still an energetic stinker? This happened to me when I got my last two cats. At the time I got Aussie, my older cat Asher was eight when I brought Aussie home, and he was NOT happy. He's 12 now and still gets on her case sometimes. Older cats can be territorial when new cats are brought into the home. Also, since Apollo is 11 he's probably tired and just wants to be left alone. I hope things have smoothed out for you by now. They're all cute cats.