Grainy pattern along Y, Bad stacking along X

Vcore 3.1 500
Spannsysteme Gantry
Full Metal Motor Mounts/Idlers/XY-joiners
Genuine Gates Belts
Quality bearing stack idlers

After Installing the Full Metal mods the prints are showing a grainy/rough pattern along the Y axis and imperfect Layer stacking along the X axis.

Belt Tension only affects the pattern to a minimum
Velocity/acceleration dont affect the pattern
Gantry is (to my knowledge) square

all axis move smoothly and arent binding.
The graphs are after lowering the belt tension step by step to 52hz over 500mm.
Sadly didnt manage to make better pictures.

I'll happily take any help, even if its just relating me to someone who had the same issue.