In some embodiments, a magnetometer mounting apparatus and system may reduce noise and magnetic flux interference by mounting the magnetometer inside a cavity in a collar that fits around a tool insert. The cavity may be sealed with a hatch cover/outsert. Another embodiment mounts a plurality of magnetometers around the periphery of a mounting ring that is coupled to the insert. Yet another embodiment mounts the magnetometers in a gap sub in the BHA. Still another embodiment longitudinally mounts the magnetometers on the insert such that a diagonal distance between two magnetometers is the greatest possible on the insert.