Control Stick vibrations under Autopilot

These vibrations are not systematic and are not that large. After noticing them during my first flights under A/P I went through the complete tune-up provided by Dynon. Since they appear from time to time and I wonder if this is common and what could be the source: trim, turbulence, altitude, ... although I have not been able to establish any correlation with any of these factors. It seems to indicate a kind of small oscillation by one servo. A fellow RV-12 owner told me he got them too and I would like to have the feed back of this group on this matter.
Thanks for your contribution.

Do you have the plane in trim? I notice that once in awhile if I don't have the plane in trim.

A little stick vibration is normal.

Being a little out of trim or having the torque settings off some could cause this.

I have small amplitude stick vibrations in pitch, but not roll. Trimming does minimize them.