Hmm.. kind of a loaded question. Any part can theoretically rattle.

But if it is general looseness of the 1911, can be slide to frame fit, bushing fit, loose lugs, etc. Not a do-it-yourself project, IMO, you can munge up your gun pretty good.

If you're really interested in the subtleties, I'd recommend Kuhnhausen's (sp?) books on the 1911 - you'll really start to appreciate what the top-tier 1911 smiths can do.

The smith will squeeze the slide rails in a vice to tighten the slide to frame fit. there is an adjustable block that Brownell sells for this purpose. It fits in the slots for the frame rails. I tis adjusted to the width of the frame rail so that you don't squeeze too far. After this is done, The slide and frame need to be lapped. When complete, there should be only minamal slide to frame play. Less than .010 of an inch. Hope this helped.

I think it's the front part of the frame. I will get that book AJ thanks.