Why does thunder make such a miserable sound?

     I'm sure that you have heard thousands thunders on a rainy day. But don't you stop to think what make that miserable grumbles? So, this is the simplest answer for it. It occurs due to the rapid expansion of air surrounding the area of the lightning bolt. If it is further explained when the lightning strikes to the ground, again a second stroke is created from ground to sky(clouds).So this activity fundamental to the rising of temperature.(This heat is occurred with the electricity generated.)With the rising of temperature the atmospheric pressure also increases. Under such a pressure the heated air explodes outwards ,compressing the surrounding air. The result of this shock wave produces a loud, grumble sound.