Hi there, thanks for the comment ! Did you manage to get the "real ending" ;) ?
In fact there is a single sound for jumps. However, as for 90% of the sounds in the game, I randomized the pitch between 3-6 values to make the sounds less repetitive (in gamemaker, this is just one line of code). The bouncing on foes sound is the same, with a much lower pitch. I always use this cheap trick :)