Suppliers put different bearing in, sometimes standard, sometimes deep groove, so it’s possible they have put the cheapest they could find . Are they noisy when you spin them in your hand (before installing)? You can feel poor quality as a first pass. If not then back to the steppers. Are you microstepping? This can make them run smoother at the expense of some loss of torque. Vary the microsteps and try again. Depending how it is defined in the units on the driver case 1600 is a fair start point