I finally got my 30X30 Longmill MK2 set up after almost a year! I live in Arizona, so it gets very hot in my garage. I finally got a Mini Split installed so I was able to finish setting up. I have a squealing noise when move the x axis when it gets about halfway along the way. That’s either left or right and not in the same spot. I have adjusted the rollers so I can turn them with my fingers. I was going to post a video but it says new subscribers aren’t allowed.
The only time I had something similar was when the screw fell out of the X-Axis anti-backlash nut (the original black delrin ones, not the new spring loaded white ones). It was pinched between the gantry and the X rail so every time it moved on X it would scratch the X rail and make a noise.
If that’s it then reinsert the screw and check all of them them from time to time to make sure they haven’t come loose again.
When was the last time you lubricated the screw? I recently did maintenance on my MK2 and a noise went away. Not sure if it was the same sound you had, but lubricated both X and Y screws (after cleaning) make a huge difference.