Yup. Backlash. The 497 will allow you to train the drives and eliminate it. Takes about 30 secs and you can do it on a terrestrial target in the daytime. Infact, you have to do it on a daytime target.
If not though it may be that you will need to remove the poor little chocolate grub screws on the drive motor gears and replace them with stainless ones.
Arthur
PS - excellent choice on the ZS
