A little more about flutter.

Air going over and under the wing is never quite smooth. As with a lot of things in nature it oscillates and this shows up in the magnitude of the pressures and velocities. This is still existing at the trailing edge of the wing where is is probably the largest.

The pressures and the resulting forces go up as the square of the velocity. So the faster you go the more force these oscillations have.

Each control surface/control system (and also the wing) has a natural frequency. It is the frequency that when it is vibrated at will cause the oscillations to increase. If you hook up a variable frequency sound maker to a taunt length of pianio string and slowly increase the frequency of the sound you will find a frequency at which the string will really vibrate.

As an example of this I have seen an aileron vibrate as the engine is throttled up and down.

With the airplane, if the frequency of the little pressure oscillations, and the magnitude of the forces that come from velocity, match the natural frequency of the control surface then you get flutter.

The loose linkages (and the other things noted by the other writers) allow the flutter don't change the frequency of the flutter but do decrease the amount of force that is needed to start it.

The stiffer the control surface is the higher frequency the natural frequency is. If you have the control surface stiff enough it will be outside of the ability of the airplane to produce it. The big slow flying hovering airplanes with almost no structure in really big surfaces are just waiting for flutter to occur.