There is most likely a strange cat outside that has got the two of them all worked up. Either a stray passing through or someone has gotten a new cat and it letting the cat roam.
Cats are so territorial another cat outside can make them feel their territory is threatened, and it is not unusual for two cats to even turn on one another when this happens.
I suggest you install some feliway plug in diffusers around your house. That will help with territorial feelings.
Also keep an eye out for any strange cats, and if you see a stray, get a havahart trap, trap the kitty and get her/him into a shelter.
Cats are so territorial another cat outside can make them feel their territory is threatened, and it is not unusual for two cats to even turn on one another when this happens.
I suggest you install some feliway plug in diffusers around your house. That will help with territorial feelings.
Also keep an eye out for any strange cats, and if you see a stray, get a havahart trap, trap the kitty and get her/him into a shelter.
