Springs don't crack. If it did, you would not have a spring right now, but there are things in there that can. Rattling noise could be a lot of things, so you need to clarify what kind of sound it makes or take it to a mechanic. Is it speed sensitive? Does it happen when you turn or even when you go straight? It could be ball joints, bad strut, damaged sway bar bushing mounts, bad radius rod bushings, damaged axles, etc...