If the new Focus' are anything like the older ones it might be the heat shields that run along the exhaust and protect the gas tank. I just can't picture that coming loose this soon but let us know.
2003 ZTW - 2.0L 16v Zetec: 9mm Racing plug wires, long style CAI, shorty header w/down pipe, glasspack for a resonator & raptor muffler
Drive it like you stole it!!