I did. I hated those AC fans. I switched them out to a ultra-quiet DC computer fan (80mm). You only need to buy an AC to DC converter and wire it up to the fans. Here is the instructions I wrote for my club (hope it is okay to post this link):
Not even close to what i need. It already has a 40mm x 28mm dc fan on the back. Its just crazy loud. I can replace with a 60 mm fan they are a little quieter and flow more air but i would like to retain the original look. The fan thats on there now sounds like a vacuum.