Hello JP.
Did you get this issue figured out?
I also have 4x Dyn4 drives with the 1300w servos (Z-axis servo has brake). They are installed on one of my heavier machines. So, it looks like I am having this same issue on my z-axis. Did you find a fix for this issue?
I'm quite certain it is not noisy wiring issues on my end, I used double shielded individually twisted pair wire with a properly grounded shield. I've tried a few things to get rid of this drift but no fix yet.
I had some issues in regards to the ENA signal being wrongly labeled on pin 3 instead of pin 15 in their manual but I contacted DMM and they fixed this minor issue. Other than this drift issue on my Z-axis, I am pretty impressed with the DYN4 servos, so far.
Thanks,
Rob