I'm having a similar problem . . I think. It's sounds like what you'd imagine a rusty spring to sound like, but only when I go over speed bumps. I've had my mechanic look at it twice now and he says everything is tight and there is no apparent play, he's checked the callipers and says he cannot replicate the noise in the garage, but it is evident when the vehicle is being driven. He thinks it could be the shock on it's way out (at 140,000 miles, I would be surprised) or it could be an Anti Roll Drop Link. But he said that there is not movement and the car feels tight, so he's recommending to do nothing and just monitor the situation as he cannot be sure where the noise is coming from and doesn't want to carry out work on one and it be the other.