Since we returned (3 weeks ago), Max has become aggressive. He has always been a super chill cat, until now. Mostly he is demanding attention by walking into a room and loudly meowing and coming up to be stroked. He lightly swats at me (claws not out) when I walk by him, if I don't stop to pet him. But if Piper comes near him, he will really go ballistic and chase her.
He's an indoor cat, and has never shown any interest in going outside - until now. He has escaped twice. We live at the edge of some woods, so we're more worried about coyotes and fisher cats attacking him than him running away.
We have Feliway plugged in to relax Sookie (she is very shy and sheds a lot, it helps and is preventing the vet from putting her on prozac).
The only thing I can think of that might be affecting his behaviour is the fact that my wife is pregnant (6 months). I have heard that cats change a bit.