We all know that a funny noise can indicate a problem with a complex system, whether that’s a car, dishwasher, furnace, or your air conditioner. But sometimes it can be hard to tell whether a sound might mean something is wrong or if it is a perfectly normal noise that you shouldn’t worry about. While it’s good to know what AC noises mean it’s time to call for repairs, it’s also good to know what noises are just the sound of normal operation. Here’s a rundown of the sounds that a perfectly-happy air conditioner might make while it’s running smoothly.