Expected
A llama with the Silent:1b tag set will make no noise at all.

Actual Occurrence
When a llama has the Silent:1b tag set, it won't make its normal llama noises, but when it spits, it still makes the spitting sound.

To Reproduce
1) Summon a Silent llama: /summon minecraft:llama ~ ~ ~

2) Summon a wolf to make it angry: /summon minecraft:wolf ~ ~ ~

3) Wait for the llama to spit, and you'll still hear the sound.