Z-Axis moving up on same layer

Hi! this is my 4th year since i bougth my prusa i3 (Ramps1.4+mega2560) and i never had any big issue untill now, the z axis seems to be moving up quite randomly within the same layer , i tryed using different stl softwares (cura,simplify3d),sd cards and is the same thing no matter the stl.
It looks like its some kind of noise in the axis but its not bcz somethimes it moves consistently just before the start of the print,just to mess up the initial heigth.
All the axis moves just fine when i do it manually with the lcd interface.
Im rlly clueless what it can be ,the fact that it moves up on the start of the print consistently kinda rules out a Hardware problem,im thinking maybe marlin configuration somehow got corrupted idk, i dont wanna mess with marlin unless is nescesary-
if anyone had some simillar issue maybe can orient me a little.

Edited 1 time(s). Last edit at 01/10/2020 05:08PM by nadaol.

... could be wear or dust in the spindles ... or the drivers loose some torque ... or both ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

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Thanks i will try clean them up but the way it moves makes me think that is a Software related issue , here a couple of videos that show the behaivor in middle print and start (the start one is just sometimes,not allways)
ZaxIssue
ZaxIssueStarting

I suspect a hardware issue
While off swap your X and Z stepper drivers. (remember to adjust the vref with a non metallic screw driver) See if the issues moves to the X or stays with Z

Hi Dust! thanks for u reply,i tried swaping the stepper drivers (y->z) and unfortunatley there was no change whatsoever,i also dissasembly the stepper motor and i didnt saw any signs of wear/dust , i will try tonight to swap the stepper's motor to completly rule that out ,if its not the drivers or the motors i cant think anything else being the problem here...

After trying everything ,2 months later i reuploaded Marlin and it works like new...wtf