in your case, you would need to hook SVC_TEMPENTITY event, since that sound is played when sending TE_EXPLOSION message (as a last param).
Code:
register_message(SVC_TEMPENTITY, "HookTempEnt");
public HookTempEnt()
{
if( get_msg_arg_int(1) == TE_EXPLOSION)
{
set_msg_arg_int(8, ARG_BYTE, 0);
}
}
}
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