RE: Questions regarding Flutter
All of the above and;
On clevises or Z bends, if there is a tiny bit of clearance, I like to add a very small amount of CA to it and hit it with kicker than flex it. Periodically I check the linkage for ANY slop and do it again if needed.
The best of servos with time get some backlash. A one time only cheap fix is to carefully open the gear case, mark the gears with a felt tip pen, Than remove all the gears (except the motor’s gear) Than reinstall all the gears 180 degrees (except the output shaft) from the way you found it. If there is a next time you’ll need a new gear set.