I think I'm experiencing a similar issue with dual extrusion on my Rostock max v3. I have a bondtech bmg etrurder on T0 ,404.6 steps per mm and the original ez extruder on T1 91.28 step per mm. On tool change the bondtech makes hi pitch noise and doesn't retract. The ez extruder does retract properly. Have you found a fix for you set up?