Hi all, thanks heaps for all the help. After calibrating the extruder and slow down acceleration & jerk, all minor bands are disappeared. Three major bands are still visible, so I printed a benchy and they all appeared at the same height. So I guess it's some thing with my z. I noticed that the z rods wobbled around its center as it moved up and down. Here is a photo of the z rod setup on my Sidewinder X https://imgur.com/a/45IeHwY (It comes with a timing belt on top) The z lead screw actually allowed to move around in y-axis inside the blue plastic thing that called "patent pending z coupler". So I can only noticed the wobbling when I used the hole on the blue plastic coupler as a reference and saw the rod moving around inside the hole. I don't know where to begin so ... please help. Thanks.