The bug
/item modify
command makes armor and offhand equip sound when you modify their nbt data.
How to reproduce
Use the data pack
Equip a chestplate
→ ✔ The armor equip sound is playedRun the following command:
/item modify entity @s armor.chest 265389:set_lore
→ ❌ The armor equip sound is played again
Can confirm that this also applies to Elytra, which will make shuffling sounds when modified.