StevieT got um for $21.99 not bad for replacements... I just thought... some members might have chillers & not need theirs & I could save a few $$$
The rear cooling fans, unlike the light fans, run 24 X 7, I am sure this shortens their life... to around two years, without maintenance... which I am going to try...
RSM 250 Cooling Fan
Did read this new post from James (Phineous)... was a great post on maintenance going give this a go too
...........
I've been through a few fans trying to find a quiet one, so far no luck. I found a couple of 50x50x15mm Thermaltake fans on eBay for $5 ea shipped, still not as quiet as I would like though.
This is what I do to make noisy fans quiet and new fans last longer:
You'll need grease, alcohol, good electrical tape and a sharp knife.
First, peel off all the stickers on the fan. If you need the info from the sticker, get it now, it will never stick to anything again. I peel them off to get access to the hub, but also because the glue will sometimes melt and the sticker will interfere with the fan or go somewhere else you don't want it.
Many fans have a rubber plug over the hub, but lately they seem to be relying on the sticker alone. Remove the plug if your fan has one.
If the fan is new, skip to the next step. If it's an old fan that sticks, you might want to try cleaning it with a few drops of alcohol and blowing out the hub. Don't use compressed or canned air to clean your fans unless you keep the blades from spinning. Spinning the blades with compressed air destroys the bearings.
Put a good amount of the grease in the hub. Use a cotton swab or your finger to squish it into the hub, like packing a wheel bearing. Spin the fan to remove air bubbles and pack it again. you want to fill the hub, so the grease is forced to contact all the interior surfaces, but not put so much that it's going to leak out later. A good quality grease is important, but I know it's hard to find anymore. I think Harbor Freight has some small tubes of Tri-Flow grease, but they tend to hide it. White lithium grease is OK if you have nothing better, but if it's a spray bottle, dispense it into a paper towel and let the solvent evaporate, then put a blob of it in the hub. Oil is not grease and will leak out immediately, so don't use it.
If your fan had a rubber plug, reinstall it now. Using the alcohol and a rag or cotton wad, clean up the grease on the surface where the sticker was and the top of the rubber plug. If the plug is bulging, squish it and clean up the ejected grease. Let the alcohol dry.
Cut a piece of electrical tape large enough you can handle both ends without touching the middle adhesive. If you touch the middle adhesive, your fingers will leave residue and the tape won't stick. Now place the middle untouched part of the tape on the surface where the sticker was covering the hub. Smooth out any air bubbles by lifting the edges and pressing the air out.
When it looks like it's sticking well, use your knife to cut away the excess tape thats hanging over the outside. You want to leave enough tape to seal well, but not have any edges where the tape can attract dirt and peel away later. Press the tape firmly in place and cut away any excess that is hanging over or not sticking well. If the tape doesn't seem to stick, discard it and repeat the cleaning and sticking with fresh tape. If it still doesn't stick, you don't have good electrical tape.
Sorry this is so long winded, but I used to work for the government. This document in current form does not meet the requirements of all applicable laws, regulations, departmental memos, presidential mandates or the random whims of power tripping bureaucrats.
also let me know if you are interested in a frag from my hammer coral 
