The fan blade is press-fited onto the fan's armature axle and the motor uses oil-less bearings.
I don't recommend oiling anything as the oil acts like a dust magnet clogging up the blades and bearings.
I do recommend using a soft painters brush and scrubbing down the blades and heat sink fins and then using some can'ed air to carefully blow away the junk. Don't spin-up the fan blades as you will damage the fan.
I would install a good temperature & fan app so you can better monitor your systems cooling. I like Temperature Gauge Pro, but others will also work.
Lastly, if you feel the fan is making to much noise then you should replace it