Dave,

Make sure your pull-pull cables are tight enough. They don't have to be super tight but they should not have slack in them when the rudder is at neutral.

I usually take a piece of plastic 3/16" 90 degree angle and glue it on the trailing edge of the rudder in the shape of a V.

The only other thing I can think of is if your servos have slop in them, most metal gears do. So you may get a a very little play from that but it should not effet flight because once the air is blowing over the rudder, it will put tension on the cables.

That's all I can think of.
I'm also assuming that all servos and trays are mounted securely and that all the linkages do not have any slop in them.

Barry Finck
Enola,PA