Phantom Flush

A toilet that refills briefly on its own every few minutes or hours with nobody using it, also called ghost flushing. The tank is seeping past a worn or misseated flapper into the bowl until the level falls far enough to trip the fill valve, so the toilet appears to flush at random. Unlike a continuously running toilet, the sound comes and goes. Confirm it by adding dye to the tank and checking whether color reaches the bowl without a flush.