stable contact force sensor

Hi all, I'm using the contact sensor plugin in ros (libgazebo_ros_bumper.so) to get the robot contact forces from gazebo. It works very well for the contact positions, but it's extremely unstable in the force computation. Also after filtering the signal it still remains really noisy. Someone can suggest me how to get a reliable contact force? Any help is really appreciated, thanks! I'm using Ubuntu 12.04, Ros Hydro, Gazebo 1.9.6