It is definitely related to the speed of the wheel (once per revolution) and from jacking the the car up seems to be the o/s/r wheel. My first thought was a wheel bearing, but there is no wobble when shaking the wheel with the car jacked up. So now I'm wondering if it could be a drive shaft but I thought they usually made a clicking noise. It's most noticeable at slow speeds, probably just because there's less to drown it out.
I've put a short video up on Youtube here:
https://youtu.be/9Lpv4hL9oUIIf anyone's able to shed any light or share experiences of similar noises, It'd be much appreciated.