Advice to fix skewed X Y axes and ringing issues
TLDR: In addition to all advice on loose belts and tension, also check the screws on pulleys, to see if the pulleys are tightened to the motor shafts (I forgot to follow the last bullet point on step 35 on the Y axis assembly manual and the screws eventually got loose).
I am fairly new to 3D printing and assembled my kit 3 weeks ago. I immediately got great prints and was really proud of having assembled the thing so nicely. Suddenly, I started having severe ringing issues and, by being a newbie, I got to a point of losing hope that I would ever get my printer to work well again. I removed my ikea lack enclosure, put the PSU back on the frame, thinking that the eventual enclosure wobbling was causing the issues and ran the calibration wizard again just to find out that from perpendicular results, my frames were now showing severe skewing results (0.24, which is the high end of scale). In addition to ringing, I also started hearing a clanking noise on my Y carriage every time it moved back and forth.
I am sharing this because all advice I got on the internet was to check for belts tension, which are valid steps, and mine were all well tightened, but it never occurred to me to also check the pulleys, to see if they were well fixed to the motor shafts.
After getting the Y axis pulley screws tightened back, my printer went back to great results, I am also attaching a picture of the benchy boat, failed prints on the sides and the successful print in the middle for reference. I hope this helps people with the same issues.