Ok so you have gone on the cheap an bought some 120mm lighted fans from eBay only to get them and find out that they make more racket than a drunken jackhammer. The amount of noise these were making when I started was not even worth measuring as I am sure it was well over 60db. When I was done it emitted about 16-17db.
I will show you exactly why they make all this racket and how to fix it. First these are also a push style fastener for the impeller shaft. Thus these can not be disassembled without a new locker of possibly causing damage to the fan.
Step 1: The Tools You Will Need
What you need to fix this drunken jackhammer is very basic.
Note: If you deviate from my materials and tools no guarantees can be made.
1. Thin Cyanoacrylate glue. I went with thin because I have found the thicker mixes hard to work with in delicate work.
2. Precision CA Applicators. I picked SIG brand because I like the tip and it allows prefect control of the CA
3. Pick and Hemostats. Hemostats are optional if you use the following alligator clips.
4. 4- Alligator clips
and as a final touch a few drops of sewing machine oil
Step 2: The Culprit of the Noise
As you can see the LED in the photos is not seated down in anyway. The power board has a tendency to come lose and partially rotate. Use a small hook pick to make sure the board is in the best possible location. Then go over the LED's and push them down onto the shelf so that you get the legs of the LED's bent down a bit.
Now you will see why I used the precision applicators for the CA.
Once things are in proper alignment it is time to glue them down.
This part you might want to test run with no glue before trying it. You get only one try. Put one TINY drop between the LED and the shelf. Then hold the LED to the shelf with an alligator clip while the glue sets. A little goes a long way. Should you pull a goof and blob out CA quick tip the fan on the side so the glue runs away from the center. This will cloud the plastic but you will still have a fan rather than a lighted paperweight.
I let mine set 10 minutes before removing the clips.
Now that this fitment issue is solved the fan emits 16db @ 12.2V.
Now add one drop of oil to the fan shaft and you are ready to go.
FOLLOW UP - If you are good with miniatures you could also use 4mm double sided mounting tape to mount the LEDs. My sight is not what it used to be so this option was out.