Servo wobbling, basic electronics question inside .. Help needed

Hi!

I just set up auto bed leveling and it could work much better.
The problem is that my servo is wobbling a couple of degrees back and forth, especially during stepper movements (z-axis).
It seems to me that some current is leaking somewhere on my RAMPS board and so the servo is inaccurate during movement.
If you wish, i could measure a bit with a scope and post pictures. Do you need a video or is it clear what I mean when I say wobbling?

The main question is how can I fix this?

Things I tried:

-swap servo .... Didn't help
-use feriite core .... Didn't help
-separate stepper wiring from servo wiring ... Didn't help


I have considered using a capacitor to prevent voltage peaks in the servo signal cable, but I have no clue if that is a good idea, nor do I know which cap should be used.
Any other ideas?

Thank you so much!