Holden Barina 2002: Squeak in the rear?

I HAVE a 2002 XC Barina three-door which has been serviced regularly. I had the suspension checked recently because there was an annoying squeaky noise at the back, especially when driving over rough uneven surfaces. I was told by a Holden dealer that there was nothing wrong with the suspension and that I should have the car checked by a panel beater. The panel beater could hear the noise inside the car, but he could not locate or fix it. Do you have any suggestions?