When I start the car and reach upto 18KM/hr, The Car makes some "TUK"

What is your question?

I can feel this sound in my accelerator pedal. Every time when I stop the engine and start again, it happens. If i stopped and move again without turn off engine, it wont happen. And I am sure that this is not related with transmission because TUK sound is coming alone without any jitter or jumping.