Question

how mosquito sounds are coming

Answer 1

Mosquitoes rub there antennae to produce vibrations which in turn produces sound.. :) Rubbing of their wings and rubbing of any organ present near antennae.. ;) 

Answer 2

There are two sources of sound from a mosquito, first their wings, and their rubbing of an organ near antennae. Those produce vibrations which are audible to human ear.