Be sure to use compressed air to blow all of the dust off the fan blades, fan body, and out of the power supply before doing any lube work. The fans can get so loaded with dust as to cause some bad sounding noise. I use a one foot length of about 1" diameter heater hose as an aid to listen to each fan to locate the one that is emitting the noise.
There is a thin self-sticking membrane sealing the motor shaft bearing on the end of the shaft opposite the fan blade end of the shaft. I pull that membrane back and use a knife point to remove the plastic seal disk underneath the membrane. I use a wire the diameter of a paper clip, dab the end of the wire in some synthetic car chassis lube, apply the grease to the bearing with the wire, add one drop of gun oil, and seal it back up with the disk and membrane (do not get any lube on the surfaces of the membrane or where the membrane must stick). If that does not restore the fan function, replace the fan unit with a new fan.
I would not use "WD-40", "Liquid Wrench" or any other such miracle oil. They have their uses, but this is not such a case.