Wither skull not obeying WitherBoss's Silent

If I put

{Silent:1}

on the Wither Boss,
it does no sound on death and hurt,
but they will still make sounds when shooting wither skulls.

As NoAI:1 no longer makes the boss health bar
to move, I wish to have a solution for that.
Although I use /kill @e[type=WitherSkull], it stll makes sound.