don't know if you have the same experience: the noisy sleeve bearing fans would be very quiet after adding grease to the axis. i have done this on six or seven fans. i tore the sticker off, used a knife or screwdriver to 'dig' that bung out, then used a toothpick to pick some shell retinax grease and fill the hole where i can see the axis of the fan, then stuck that bung back and stick some electronic tape so that the bung would not come out easily. it is really quite! but from my experience those liquid-like lubricant such as WD-40 doesn't work well, the fan would becomes noisy again after a few month - i think it's because the oil dried quickly. but if you use some toothpaste-like grease [don't know how to tell it in english] such as the can of shell retinax i used it would last very very long. i added the grease to the fan in my PIII box seven years ago and it is super quiet until now [the box runs 24/7]!
just my little experience.