What was the mystery part?

Hi, over the last two weeks my 1999 1.2 vauxhall corsa was making a rattling noise whenever i went over bumps/potholes in road which sounded like it was coming from the boot. Then, yesterday I had my window down and the noise was even worse and sounded like it was coming from underneath the car. Today, I was driving up motorway and something broke off and as i watched it bounce away in my rearview mirror it looked like a spring or coil that was fatter in the middle but because it was motorway i couldn't stop. I stopped at kwik fit on way home and they said there is nothing wrong with suspension and they havn't a clue! can anyone help?!

Thanks