FOF Crumble sound plays from the floor of the sector, rather than the FOF itself
In EV_CrumbleChain in p_floor.c, the played sound uses the sound origin of the sector the FOF resides in, which has its z set to sec->floorheight.
In EV_CrumbleChain in p_floor.c, the played sound uses the sound origin of the sector the FOF resides in, which has its z set to sec->floorheight.