This can happen if, say, you have rudder pedals, and a joystick with a twist axis. By default, the twist axis will be assigned to control the rudder. Meaning you have two controllers assigned to the rudder. And they’ll sort of randomly activate. Make sure you have no other controllers assigned to control the rudder axis other than the controller you are using for it.
This can also happen if you assign the rudder key to the controller axis instead of the rudder axis option. Make sure, if you have a rudder controller, that you have assigned the proper axis for controlling the rudder.