I wouldn't just drop lubricant on the fan. If the fan is clogged with dust or nicotine it will slow it down even more.

If you can access the fan use some 91% (or 91-99%, do not use anything with a lesser percentage as they can be conductive and if accidently dropped onto a system / logic board can cause electronic components to short out) Isopropral (rubbing / the white NOT green stuff) alcohol and a brush to clean away the dust and debris then add about 2 drops of 3 and one oil down in the center where it gets inside of the fan housing.

If it still makes noise, you probably have a bearing going out - these fans spin hundreds of revolutions per second and will simply wear out ... in this case, replace it, the fans only cost a few bucks.

give it a good oiling with some grease ..don't use WD40 it good but lasts only a few days ..give it a good clean as well.

Maybe the fan is heavier because of the dust on it