If the fan is still not working correctly you may need to oil up the fan.
Well there are a couple of things that could be wrong.
One would be that your hard drive is getting old and starting to die out or it could be just a case or power supply fan.
First you will want to open up your computer case to see where the noise is coming from.
Now there are a couple things that could make it so you fan isn't working correctly one could be that it is clogged with dust and the other could be that it is not being lubricated enough.
If the fan is clogged with dust you will just want to go pick up a can of compressed air (do not use a normal air compressor).
Once you have the can of compressed air you will want to blow all of the dust out of the fan while keeping the can upright.
After you have all of the dust out you just need to put the fan back into the case the same way that you took it out. Take your can of compressed air and blow into the rotating fan to get the remaining dust out of it.
If it is your hard drive that is making the noise then you may want to consider backing up most or all of your stuff because the drive may or may not have much life left in it. You have two options here you can either just go out and buy a new fan (they are pretty cheap -) or you can choose to clean the fan.
Cleaning the fan is actually a really easy process from what you may think it may be.
First you will want to turn off your computer completely and then unplug the power cord so there isn't any power going to the computer.
Now you will need to take the fan out of the case (usually just a couple screws).