Hi Les! Here are some suggestions to try to see if you can stop the creaking (which if not accompanied by pain will most likely disappear with one or all of the following suggestions).
1) Try doing a 5 minute additional warm up prior to starting the workout, then do 5 minutes of additional stretching after doing the workout.
2) Only do this particular workout once a week and not prior to or following a leg or step workout.
3) Modify any super high impact or deep bending or squatting movements in the workout.
Good Luck!