Currently, a player equipped the backpack will see the subtitle “Leather armor rustles” (strictly speaking, the corresponding string for the translation key subtitles.item.armor.equip_leather).

This might confuse a player because hi/she is equipping the Backpack, not the Armor.

I suggest to create new subtitle ID, such as subtitle.backpacked.backpack.equip.

Unfortunately, the subtitle is tied to the sound and cannot be changed. I would have create my own sound, which is something I may consider for the 3.0.0 version of the mod.