If you equip armor, including turtle helmet and elytra, in your inventory or by using a dispenser, you will not hear the armor equip sound. However if you equip armor through your hot bar you will hear the armor equip sound.

• Steps to Reproduce:
  1. Open your inventory
  2. Once in your inventory, put armor on your character

When you put armor on your character you will not hear the armor equip noise.

You should hear the armor equip noise just as you do when you equip it in your hot bar.