Do your kitties seem to find the warmest places in the house, too?
Especially now that fall (well, winter in Wisconsin) has brought colder weather, I find the kitty sleeping directly next to (and sometimes blocking) the heating ducts. He also loves finding a bright patch of sunshine to lay in during the day. My mom has always had an electric space heater in her apartment when the weather cooled down, and all of her kitties have laid right smack in front of it, to the point that their fur is HOT to the touch. (Mom always said the kitties were "cooking" in front of the heater.) For her black boy kitty, Phil, she even has to put the space heater on IN THE SUMMERTIME occasionally because he just loves to cook. My (RB) girl kitty used to sleep on top of the clothes dryer whenever it was running - I even opened up the electrical panel and disconnected the buzzer on it because it scared her (and me, too - LOUD!)