My central A/C woke me up because it was sqeaking so loudly. I hit the side of the unit and it got better but started again. I turned it off and took the cover off. It is dusty in there. Can it be oiled so it will stop and I can sleep?

It could be a lot of things.
* Yes, look for an oiler (very small hole on the motor) where you can put a half dozen drops of furnace motor oil.
* Also, though, check your motor mounts. They may be coming loose.
* Could be the belt slipping, too. Check to see that it's in good condition.