I have a S800 EVO Z15 GH3 and have the exact same problem with vibrations in arms, tried to change gains but still the same.
This EVO is from the first batch with no motor dampers, i have contacted my reseller waiting for an answer.
My footage is rock solid, but the vibrations concerns me.
Different settings
I got the same problem and found out that you can change record setting to 1080i and a lot of other settings but this is not were you have to change it.
You have to set monitor (HDMI) out setting to 1080i, then it works:)