A study by an australian university suggests people's ears play tricks on them when they drink too much coffee.
Researchers looked at a group of volunteers who were told to consume high levels of caffeine and listen to a white noise machine.
Volunteers were told a song would play in the background, and if they heard it, they should press a button.
The song never actually played, but several people actually thought they heard it.
Researchers say five cups of coffee a day is enough to trigger the same effect.