Apparatus and method for detecting metal disturbance during a medical procedure has a probe having an insertion tube, a joint, and a joint sensor for sensing a position of the insertion tube. The joint sensor has first and second subassemblies as magnetic transducers. A processor is used for measuring force using the joint sensor, and a threshold field value stored therein. The processor receives and processes one or more signals output by either the first and second subassemblies responsive to a magnetic field so as to detect changes in a position of insertion tube. The processor compares the sensed field value to the threshold field value and identifies a presence of a metal object when the sensed field value is below the threshold field value.
