Rat Rig 500 Hybrid Y-Axis jumping and loud noise

I have built a few RR V-Core 4 500s but have never encountered this before. The X-axis runs smoothly, but the Y-axis moves in the right direction with many jumps and noises. I have pulled apart the motor mounts and checked if there are any issues with the bearings, but it looks all fine. I have no explanation for it and need some help to sort this out. Any help is appreciated.