I've just replaced fan in my Avid HD Omni interface. I previously replaced a fan in HD I/O with Noctua. I decided to go with the same brand again. NOCTUA NF-A4x10 PWM was the one I used. It's working quietly now but when the FAN menu is set to AUTO I get FANERR message on the LCD scribble. I set it to ON and there's no error coming up, the fun runs on its full throttle but it's very quiet, so that's fine.
I've been running the interface for a few hours now and it doesn't heat up more than it did with the original noisy fan.
There's an article on Pro Tools Expert which might help but I just went for it without actually reading it - it's that easy. http://www.pro-tools-expert.com/home-page/2014/5/28/replacing-the-fan-in-an-avid-omni-tear-down-with-pictures.html