I have a Luxaire central AC. I works fine, it just makes a sound like the fan is hitting something, but its not. What else could be causing this ratteling sound? Is there a way to lubricate the fan?

It depends on the type of blower you have. If it is a belt-driven blower it could need a new belt. Unplug it and slide it out and you can then see what the problem is. It should be cleaned and oiled once a year, anyway. You could have a wire slapping around in there, too. If a wire comes loose when a wire tie comes loose it will also make noise and can cause real problems. I recommend that you get the coils-inside and out-cleaned and oil the fan motors once a year. You should be able to find the problem then. Make sure you wash out the coils with foaming alkali coil cleaner and wash out with 1500 psi electric pressure washer, if done right, and clean the blower, too, because 1/16" of dirt in cups of blower causes a loss of 30% efficiency.