Melissa Saenz at Caltech in Pasadena was tipped off when a visitor looked at her screensaver, which made no noise, and said, "Does anyone else hear that?" She quizzed him and found that his experience had the hallmarks of synaesthesia: a trigger through one sense was giving rise to a sensory experience in another. It was automatic and her visitor had experienced it as far back as he could remember. via New Scientist