Yes, the answer is gravitational anomaly and agricultural equipment and surveillance drones actually pursue such gravitational anomalies. Because both of those machines require GPS system to control them; to give them exact location at exact time. Gravitation makes clock slower and GPS system uses calculations of General Relativity to keep time matching with the ground. But gravitational anomalies can disturb those calculations used in GPS system and make those machines to lose or misunderstand (roughly speaking) their positioning and timing commands.
Edited to add:
One can find this in 'The Science of Interstellar' by Kip Thorne
The GPS system that Cooper has adapted to control harvesting machines, as they roam through corn fields, has also gone haywire, and a bunch of harvesters have converged on his farmhouse.
He attributes this to gravitational anomalies that screwed up the gravity corrections that any GPS system relies on.