I think you are merely hitting the maximum movements of the control surfaces.

With most computer controlled radios, you can set the "end point" adjustments to prevent you from bottoming out the servos, eliminating the noise you hear as the servos try to push past where the control surface is permitted to move.

On non computer controlled TX equipped trainers, you cannot set an end point adjustment.

Many people just fly the planes this way as you rarely ever max out any control...

However if you wanted to you could adjust the linkages or change the control horn holes used to stop this.