Are you surer that it's actually tubing (i.e. hollow), rather than solid metal. The last time I heard a big bang from under the car, and discovered a (solid) piece of curved metal, it was from one of the springs. Fortunately, they're fairly cheap to replace!
If it is actually tubing (and therefore not from a spring), what sort of diameter are you referring to? Is it wide (like an exhaust pipe) or much narrower?