It's the tranny put in the mid-01 and up Mustangs.
It's a Ford design made by tremec.
They have a problem where they tend to be noisy going into 2nd gear when cold. Ford has just released a TSB that will fix the problem in factory 01-04 cars...but it's gonna cost you a lot of money to fix your trans on your own. I'd wait for a post-fix trans