I'm not sure why you are having such a problem with the chopper. I do seem to recall the first time I replaced one I tried to install it in the back groove instead of the front one. It doesn't fit that way
. The bad choppers I've seen, the blade had fallen off and the screen was completely clogged. If you hear rattling, it's probably just something knocking around in there. It may pump out on it's own or you can take it apart again and clean it out. Whenever I take one of these apart I have my shopvac ready and give it a good cleaning.