In my rig I have lots of silent fans (140mm silent fans, 120mm silent fans), I did a review fitting Knox silent Fans a while back, as part of that same rig however I have a Corsair Airflot RAM Cooler:
I've never really liked this addition, but it does serve a good purpose, cooling my RAM significantly, but the fans are small and loud, very loud, as it has aged however, it is getting terrible.
I had heard some users mention this unit making noise, but they didn't have it fitted to Corsair ram, so I assumed it was just their unique problem. Well I do have Corsair RAM, I purchased the RAM and cooler as a kit when I put the current Core i7 rig together myself
Over time, I've heard it making a bit more noise than normal, but last night whilst working, I had to actually open the case and pull the power cable on this, it was grinding, vibrating and generally grumbling like crazy, as I pulled the power on it my rig became almost silent instantly, and totally silent once I'd shut the case back up again. This little fan had been causing such trouble.
I actually trouble shot this even more, and using my finger bravely, stopped the fan spinning (don't do that at home folks!), and figured out it was the fan to the top most position which was making all the noise, the other fan was silent...
I'm thinking after a server back up of my code, and doing some work on the house at the weekend, it might be time to strip the PC down and clean it, and see about replacing this fan unit.