i have one fan that died.. it spins very slowly and makes a horrible rattling noise.. this is the fan that started making noise before i oiled it.
ive since oiled all my fans.. a few of them were completely dry..
i suggest everyone to peel the sticker off and put a drop of oil on the bearing.. let it soak in for a few minutes and run the fan face down for a few.
Be careful.. oil can mix with dust making some sort of paste and block the bearigns completely. Some bearings are designed to run dry (don't know if these are the case).