Just as a bit of an update on this, it turned out to be the 3/16" C clip that was missing just like like was suggested.
Don't know how this came off, where it went to, or even if it is rattling around inside the car somewhere...couldn't see it anywhere though.
I didn't have any of the actual parts, but I found that a modifed 1/8" E clip worked a treat. I just rounded it off with a dremel to make it more C shaped - fiddly but worth it.
Now everything is back as it should be - and no rubbing sound anymore.
