It's likely that the bearings are worn out on your fan. I don't believe there are many fans that allow you to easily add a drop of oil; you would have to take the fan apart to get it in the right place. The oil would only temporarily fix the problem anyway. The first thing I would check is to make sure all the attaching hardware is secure. If loose hardware isn't the problem, then it's relatively easy and inexpensive to replace.
Some CPU fans are matched to the heatsink, and it's possible that yours is one piece. Most CPU fans and heatsinks are sold together anyway.
My computer for some reason is making a buzzing sound once it's been on for a few hours.I can tell it's coming from the fan because if I just touch it right in the center as its spinning the noise stops.Is it possible that maybe a bit of oil might help it?. Nothing changes as far as performance at all when it starts this humming or buzzing so I'm hoping maybe theres a quick fix, like I said maybe a bit of oil.What do you guys think? Also one other thing, it seems the fan is attached to the heatsink as if it's one unit, does that sound right or should there be a way to seperate the two.