I know what you mean about the chatter. I had a metal box on the back of mine and it annoyed me so much that I switched back to my topeak bag. I got a piece of foam cushion under my batteries. It seemed to help stop the batteries from jarring around and loosening bolts on my rack. I also stuffed some newspapers in my bag.

As far as battery setups go...I'd say bags or plastic setups > metal boxes .