Scientists have solved the riddle behind one of the most recognisable and annoying household sounds: the dripping tap. And, what's more, they say squirting washing up liquid in the sink solves the maddening problem in seconds. Using ultra-high-speed cameras and modern audio capture techniques, researchers showed the'plink, plink' is not caused by the droplet itself hitting the water. Instead it's the waves, or oscillation, of a small bubble of air trapped beneath the surface. Researchers from the University of Cambridge's department of engineering used an ultra-high-speed camera, a microphone and a hydrophone to record droplets falling into a tank of water.