PROJ ISOUND

PROJ_ISOUND is a defineprojectile property used to play a sound when a projectile impacts a surface. This is ignored on bullet projectiles.

Syntax is:

defineprojectile <tile number> PROJ_ISOUND <name>

Where <name> is the name of the sound you wish to play.

Set -1 to nothing (not zero because if you look at DEFS.CON define KICK_HIT 0)