I have the same issue on the N/S. From inside the car it sounds like the rear bush on the wishbone (judging by the location of the sound) but it had it's MOT and nothing was found. I asked about it and the guys checked it over again, pushing the shock up and spring, leavering the wishbone, ARB & top mounts too but still nothing. If anything, the O/S rear wishbone bush is wearing but it's as quiet as iit should be. I am contemplating getting a new arm as it's annoying me loads!