I'm glad you were able to get yours replaced so easily with one that didn't rattle.
I was finally able to silence mine by applying a small piece of tape on the bracket where the screw is on the inside (I know, totally jury rigged) but it seems to work as long as I don't open the flash and you can't see the tape anyways. Fortunately, even on my D80, I probably used the pop up flash less than 10 times since I've owned it, so it shouldn't be a problem. Seeing that there are others that have the same issue, I'll just live with it like this.
I also did try tightening the screws some on the flash which didn't help at all since the screws were already tight.