He will attack his brother, and when I break it up he flops down and howls and meows for a while. He doesn't want any affection shown during these times. He does have pica (eats fabric) but we have been keeping all fabric out of his reach. He also has flatus occasionally. His appetite is fine and he's drinking plenty of water. His bowel movements are fine (no diarrhea). After these aggressive/howling episodes he appears pretty much fine. Any ideas? He and his brother go to the vet 2x a year and so far have been in excellent health. I do have Feliway diffusers in the house. However, I don't want to mask any possible condition with the effects of the Feliway.