Backpack Sound Bug
Have you tried stripping off naked and seeing if it still does it?
The sounds your character make are actually derived from your clothing parts; if you’re wearing heavy armour on your legs but padded shoes, you’ll here it scrape and clank when you bend your legs, but your footfalls will sound soft, it’s a very clever system for immersion.
A lot of armour parts though unsurprisingly may be annoying, like running about in full plate will clank and scrape a lot with every little movement, while some of the light armour sets have jewellery and adornments you can hear shake and clink as you move.
It’s more likely you’ve upgraded to new armour that has a different ambient sound to your old set than it being tied to the backpack you once equipped
Garnished Toast
Ah sorry, I did not make it very clear but yes I did try that. The sound is still being made without any armour, weapons or accessories on at all.
I know the armour sound that you speak of, and that is ideally what I would like to hear! The kind made by the “invisible” backpack I seem to have on is a lot more audible. It sounds like marbles rattling around in a metal tankard.
Also, it is worth noting that the sound continues when switched to the cloth-like town clothing set. However, when I change back to my armour set, the sound disappears only to turn back on after a vista, cut-scene or re-log.