[BlackGT]

It could be one of several possible things making the noise, In the Mach's it is most likely the rack bushings as everyone is saying. In my GT and also my Bullitt I was getting a similar creaking to the one you describe and I replaced the rack bushings with Poly ones and that did not solve my noise, It actually turned out to be outer tie rod end in both cases. However on my Mach 1, same noise and I got it to go away by simply slightly loosening the rack bushing bolt. But you could always replace the rack bushings just for the heck of it, they are cheap and easy to do and yes make sure you replace the front and back bushings you can also shorten the metal sleeve slightly like some TSBs tell you.