Love my JBL in-ear wired headphones but I can only use them when sitting still. When I walk with them they 'rustle' like crazy (don't know how else to describe the sound)

I think you're talking about microphonics:

https://zikman.audio/blog/cable-microphonics-what-it-is-and-...

Also sometimes called the stethoscope effect.

I think strictly speaking, this isn't actually microphonics, because that means that mechanical noise causes electrical noise, which then results in audible noise, whereas what is happening is just transmission of vibrations up the cable into the ear.

Anyway, it can be fixed with better cables. They don't have to be fancy (they don't have to be the 349 euro cables that site is selling!) - i have a pair of KZ ZS10 Pro X earphones, and using the stock cables, i don't get rustling through those.

(more generally, i have an embarrassing number of Chi-Fi earphones, and don't get rustling with any of them)