I have come across a trick that works great to help keep older computers running quieter. I often find here in the shop that a computer comes in and has funny noises coming from one or more of the fans. As most of the time a fan is more then the cost of my lunch I often try to keep them going with just little bit of work.
Fan Trick
Get some 3inOne oil or Marvel Air Tool Oil
Unmount the fan from whatever case or heatsink it is mounted to
Turn the fan over to the bottom and one should find a sticker
Peel back the sticker and there most of the time either the bare shaft or a rubber stopper
Put two to four drops of oil on the shaft and let draw into the fan shaft
Clean up any excess oil
Replace the rubber stopper and the sticker (If the sticker will not stick then a piece of tape will do)
Remount fan
Now you should have a much quieter fan.
Well happy computing and keep those old computers running longer.