anyone know why thunder even makes a noise?
A bolt of lightning is supposedly 5 times hotter than the surface of the sun. That is sort of believable, because to spark something a few miles, it takes some massive amounts of energy. Massive amounts of energy means massive resistance, and massive heat.
So the air is superheated with this giant spark. If the 5 times hotter rule is true, that means that the air gets to over 10,000 degrees. If you remember PV=nRT from chemistry (even if you don't) you know when air gets heated up, it expands.
When air gets heated up a lot very quickly, the air expands a lot, and very quickly. (Explosions also expand air a lot, and very quickly.)
Sound is created by changes in air pressure. The Explosion effect from a lightning bolt is more than sufficient for us to hear it.