Why is my laptop fan suddenly much louder than usual?

I've cleaned the fan and the heatsink. As I type this there is not a single spec of dust inside my laptop. I always use a cover when it is not in use. I've only had it a year, yet the laptop has suddenly become very loud. It is a magnetic bearing fan if that helps. I've considered turning on the laptop after taking the fans blades off to see if it is a matter of friction and needs lubricating, i'm guessing that's safe to do, is it? If it needs lubricating, what kind of lubricants are ok to use?