http://wowdev.wiki/index.php?title=Talk:M2/WotLK#On_animations
There are events that play sounds that are given by various DBCs instead, like footsteps. To quote a few, There is $AH[0-3], $B[RL][0-3], $BRT, $CSD, $CSS, $DSL, $DSO, $DTH, $ESD, $FD[1-9], $FDX, $F[LR][0-3], $FSD, $GC[0-3], $GO[0-5], $HIT, $R[LR][0-3], $SCD, $SH[LR], $SMD, $SMG, $SND, $TRD, $WGG, $W[RL][0-3], $WNG, and probably some that I forgot, that will all play a sound.
Where did you add the value ?
Is not something like that supported by pymodeleditor?
Anybody can make a tutorial How to add $SND event to an M2 model?