The Bug:
Horses play armor equipping sounds when their armor item is read from NBT.
If a horse has armor equipped, it'll make noise when you change its NBT data.
Steps to Reproduce:
Summon a tamed horse that has some armor equipped on it by using the command provided below.
/summon minecraft:horse ~2 ~ ~2 {NoAI:1b,Tame:1b,ArmorItem:{id:"minecraft:diamond_horse_armor",Count:1b}}
Modify the horse's NBT data by using the command provided below and listen closely as you do this.
/data merge entity @e[type=minecraft:horse,limit=1,sort=nearest] {FallFlying:1b}
Take note as to whether or not horses play armor equipping sounds when their armor item is read from NBT.
Observed Behavior:
Horses play armor equipping sounds.
Expected Behavior:
Horses would not play armor equipping sounds.
I can confirm that this is an issue. Also affects 1.17.1 and relates to MC-123450. The expected behavior would be that the "Horse armor equips" sound doesn't play upon running this command.