Can a sensor make a car tick from the bottom?

The question is somewhat vague, not knowing the make, model or year of the vehicle. That said, the most common ticking noise from the bottom of a vehicle is the fuel pump.. It is electric and usually located inside the gas tank.. It does in fact make a constant "ticking" noise when fuel pressure and volume is needed to run the engine. The pump is activated instantly when the ignition key is turned to the on position to build fuel pressure at the injectors for initial start.