OP: "....attributed to flexing of airframe with increase in forward speed, in which the all composite body of the aircraft gets slightly compressed due to aerodynamic forces on it, which in turn leads to an un-intended movement of control rod (without any feedback on the collective lever) leading to increase in pitch on the blades resulting in increase in torque."
Check tie rods and gearbox mounts etc, sounds disturbing.
Torque should decrease with fixed lever as speed increases to 120kph