why is there lighting when it rains?

rain is not necessarily followed by lightning. As moist warm air rises, it cools down by adiabatic effect with altitude and when moisture condenses, it forms clouds. If it rises even more, the droplets get so big that they come down as rain. If it keeps rising to the top of the troposphere, it gets so much friction that the static electricity causes the lightning. Sometimes the rain goes up so much that the droplets get so big and freeze into pellets of ice. When it finally comes down, it is as hail.

The thunder from the lightning can, indeed, get very loud. Perhaps you live in a place subject to many thunderstorms. But, otherwise, most people think that a local thunderstorm now and then, is okay.

Did you know that the lightning gets so hot that the air turns into plasma? This is why it is so loud as the air expends rapidly. It also turns some of the oxygen (O2) into ozone (O3) and that is good because we need the ozone layer to protect us from dangerous UV radiations. It also turns some of the nitrogen in the air into nitrate and that is good because nitrate is a natural fertilizer without which plants and trees would have difficulties to grow.

So, look at the positive sides of the thunderstorms! ;-)

It's lightning.

And the noise after the lightning is called thunder.

Lightning is about friction and static electricity and a sudden multimillion volt discharge.

Keep hearing protectors in your pocket.