I get an engine when I using ent_playsound in combination with the "pXent_getspeed" function from "car.c" in gamestudio folder ("\include\"):

What sound file you are using doesn't matter. It crashes with wav and ogg. The file is also not broken, I've tried many different sound files, even some files vom gamestudio folder.

Code:
#include <acknex.h>
#include <ackphysx.h>

SOUND* snd_test="test.wav";
var snd_hndl=0;

//this function is from /include/car.c in gamestudio folder
var pXent_getspeed(ENTITY* ent)
{
	VECTOR vSpeed,vDir;
	pXent_getvelocity(ent,vSpeed,NULL);
	vec_for_angle(vDir,ent.pan);
// speed in km/h, assume 40 quants = 1 m	
	var speed = vec_dot(vDir,vSpeed) * (60.*60.)/(40.*1000.); 
	if (abs(speed) < 1) 
		return 0;
	else 
		return speed;
}

void main()
{
	physX_open();
	level_load(NULL);
	
	ENTITY* ent_tmp=ent_create(CUBE_MDL,nullvector,NULL);
	pXent_settype(ent_tmp,PH_RIGID,PH_BOX);
	
	wait(-3);
	
	while(1)
	{
		pXent_getspeed(ent_tmp);
		
		if(!snd_playing(snd_hndl))
		{
			snd_hndl=ent_playloop(ent_tmp,snd_test,100);
		}
		
		wait(1);
	}
}