@Step_Cia if the problem is stepper rippling due to missed microsteps like I suspect, an 8825 will make it considerably worse. An SD6128 driver from Panucatt would be a better thing to try. Just have to make sure you can set the microstepping properly.
i think it``s related to the geometry of the timing belt versus the pulley. look at them carefully and try to see if they wobble.