Get that audio interface tested Doc
Doc a few people have had this issue with the saffire pro. Not sure if this helps any but we have 2 saffire pro 40s and an Octipre and every now and then I have to go into the Saffire mix control and change the clock setting to ADAT on our system. Still haven't figured out why it changes to "internal" on it's own. Also try changing the hardware buffer in DAW software. Cracks and pops are normally caused there. Maybe switch it to adat then back to internal. id suggest taking the saffire pro into your friendly favourite music shop ask them to test for you. At least you will then know if its your audio device or your computer. if its a faulty audio device at least you will know one way or the other.