When the ball hits the back of the net, the sound is like no other. With soccer, you can see a play developing but the outcome is uncertain until it's in. Something about the uncertainty of the play and deveopment of a goal that makes the sound of the fans so much more ecstatic.
There are really two different sounds for a goal. When I started following the Champion's League a few years ago I realized that the crowd in Europe sounds different from the crowd in England upon seeing their team score a goal.
On the continent they scream "Gol!"
In England, it's a massive "Yeah!"
That's my favorite sound.