why I hear a buzzing sound from my car when I press indicaters?

Answer 1

Making a clock or relay loose.

Answer 2

It is intentionally made to sound like this....tak.....tak.......tak......tak ...in case:

a. you were not able to see the indicators blinking (due to direct sunlight on the dashboard or excessive brightness in the cabin) and you have already straightened after negotiating a curve...(this situation arises when the steel balls (inside the steering wheel combination switch) does not go back to the 'grooves' (say...'home') and the blinkers keep on blinking. One looks like a fool or just another driver may misinterpret your driving direction).

b. The dashboard indicator bulbs are not working, though the blinkers outside are working. That means the outside blinkers are blinking but inside you don't get the idea due to fused bulbs.

This is made possible by a special relay switch in which the contactors are made to make this noise.