have a total of 4 cats, ranging from 3 years old to 4 years old. They have gotten along fine, up until a few days ago. Two of them (SF and NM) aged 7 years and 4 years respectively have suddenly started some nasty and loud fights. Of all 4, they were the two that used to barrel around the house together (I called it race track kitty), they slept on the bed with me, etc. A few days ago they had a fight, deep meows, some screeches etc and then everytime they SAW eachother after that, they would let out the deep meow. They had another "spat" at 5:00 this morning, same reactions. They are walking around "on egg shells" right now. I do have feliway diffusers in my house and have had those for quite a few years, nothing has changed (I haven't moved, I haven't bought new furniture, re-arranged the house, no one new moved in or out, my schedule hasn't changed...NOTHING HAS CHANGED!!). I just can't figure out what happened to cause such tension and aggression between these two....I don't even know what to do when they are looking at eachother growling those deep sounding noises...HELP!!!!!!! How do I get them back to a "happy" place!! It is very upsetting to see them both so upset!!