Time: 4:48 (he looks backwards and like extend his jump) What is this trick with a sound and how do you perform it?

That is simply cancelling sunsetter by pressing jump before you slam down. They used first person to turn around because canceling sunsetter gives you a bit of height and backwards momentum.

Omg I didn't know there is a sound when you enter/exit first person (didn't know there is first person at all lol) and thought it's like unique trick. Thanks!