The motor current adjustment pots on the stepper motor drivers are all set to the middle position from delivery. During operation I encountered from time to time knocking sounds from the extruder motors (especially on high printing speeds) and also I had a few lost steps of the delta tower motors.
So I increased the motor currents and had since then none of the reported problems any more.
See the image below:
![](https://bechele.de/wp-content/uploads/2022/07/139-1.png)