E31 'Clicing' from Rear Wheel

[Job38]

Have had the windows down today and noticed a 'clicking' from the N/S rear (I think). Clicking increases speed with road speed.

It's not tyres, as I've just changed the rears.

Have had it up on a jack but can't spin the rear wheel to check, presumably this is the LSD?

Any Ideas what it could be? Doesn't sound like bearings, sounds 'lighter', if you get my drift......

[E30M3SE]

Stone in tyre, brake dust shield, handbrake mechanism, driveshaft are all possibilities.