Why does water poured from more distance produces greater sound?

It is traveling faster when it hits the object as it is going through a greater distance as it accelerates at the acceleration of gravity. More speed means greater energy and hence a louder sound when it impacts.

As Newton would say "Force equals mass times acceleration" so the if water is falling 2 feet it doesn't have the time to accelerate and build up much force behind it. Where water falling 40 feet over a water fall has plenty or time to build speed as it accelerates while falling it builds up a higher Force which creates a greater noise upon impact.