MBPr Dock bar jitter

[Dadou]

Hi all, new member here.

I'm experiencing a weird jittering sometimes in the dock bar and in the status bar where they both seem to expand and resize on the right side, specifically on the little line that separates the trash can from the dock and in the clock area as well.

This seems to have been occurring occasionally but frequently since El Capitan update.
Does anyone have a clue about what it is and how to fix this?

I am using a early 2015 MBPr 13" 2,7 Ghz i5 8Gb RAM 256Gb SSD

Thanks in advance