The resilient bar might be fixed incorrectly (wrong orientation) or the incorrect length of screw may have been used when fixing the plasterboard.
Resilient bar should be fixed horizontally with the bars perpendicular to the metal studs, with the fixing flange generally at the top of the bar. Consideration needs to be given to the detailing around openings and White Book Chapter 04 Section 05 contains examples of how to set out the Resilient bars around doors etc.
It is important to ensure that the correct screw length is used when fixing plasterboard to Resilient bar otherwise it could result in the screw coming into contact with metal stud. This will reduce the sound insulation performance of the system by creating a bridge which will conduct sound. Resilient bar is 16mm deep and the appropriate Gyproc screw should be selected to penetrate only 10mm through the metal. It is also important that services, fixtures, etc, do not form a bridge between the lining boards on each side of the partition.