You sure about that?

If the vertical stab is infinitely stiff, then with no linkage, the rudder will fair into the relative wind.

For flutter to occur (in the modes I am familiar with) there must be an "energy" coupling between the fin and the rudder. These forces would transfer between the flexible vertical stab and the rudder through the hinge. It seems that the force on the rudder will act at the hinge point and create a torque through the CG of the rudder.

This is why we balance rudders at the hinge line, so that any force on the hinge will NOT generate a torque and move the rudder. If the CG and the hinge are coincident, then the moment arm is zero, and no torque is generated.

When they are not balanced on the hinge line, any movement of the fin (from flexibility, a gust, whatever) will cause a torquing moment, between the hinge and the CG of the rudder

Sorry if I messed this up, I thought it ws how it worked