Speed Wobble
First I would verify that the tiller bolt and hinge bolt were tight.Next, check the rudder by trying to move the rudder fore and aft, and side to side. If you have play, it is very easy to fixed by dropping the rudder and wrapping the rudder post with a sheet of teflon. Put just enough wraps of teflon on the rudder post to make the rudder snug.good luck, bob