Lately I've been noticing when my electric radiator fans come on, there is a slightly louder noise than normal. The noise in only when the fans are running. My question is why are there two fans? If one goes out will the car overheat? Are they difficult to replace? When the motor had been turned off and the engine cooled, I spun the fans by hand and the one turns a little harder than the other one. I'm wondering if that could be why it's getting louder, are there bearings in the fan that could be wearing out?? thanks for any help.