Sounds like the servo is in a bind. Take the servo arm off and move it with the transmitter and see if it still flutters.
Also I see that you are using digital servos. I dont use them but my buddies at the club that do have the same thing on almost every plane I see. The servos flutter for about 20 seconds after the TX and RX are turned on.

You may already know all of this, but this I what I would look into.

Heres what I would try if the servo looks good without the servo arm on it.

1. Put the trim on the transmitter at the neutral point.
2. With the sticks on the transmitter in the neutral position and the TX and RX on, put the servo arm on where it is perpindicular to the servo, this should give you max travel in both directions.

Are you using a computer radio?
If so, switch to high rate and back the endpoint on the rudder down to about 25% on left and right throw.
3. Get on the Endpoint screen and go to the rudder EP setting.
4. Give full left rudder and while holding left rudder start cranking the endpoint up giving you more throw. If at any point the rudder starts to shudder, OR stops moving while you are cranking in EP, back off of the EP till you see the throw moving towards neutral again.
5. Once you see the rudder moving again stop and add 1% EP at a time, but stop just before the servo is mechanically limited, either by the rudders ability to move or the servos throw limit.
6. Give full right rudder and repeat the process.
If you arent getting as much throw as you want you on ANY surface need to make sure that the control horn holes where the clevis clips on are directly above the center of the hinge line. If they are back behind the hinge line you arent going to get max potential throw. Also if the hinge gap is too tight or has glue in it its gonna limit your throw. On your U CAN Do if the rudder and elevators are hinged up and the control horns are mounted correctly you should be able to get 45 degrees of throw no problem.

If you arent using a computer radio, check your hinge joint clearances and control horn positions and just take what the transmitter will give you.