As the water droplets fall, it Potential energy decreases and according to the law of conservation of energy, when it hits the floor some of its potential energy gets converted into kinetic energy and the remaining as Sound...... read more
So water flowing in a pipe makes some sound but turning at a corner in the pipe it makes more sound,as resistance to flow, the energy has to go somewhere, heat, sound, vibration. The water escaping a pressurized system at the tap, more sound. read more
a low pitched sound growing in pitch (like "Doo-eeeee" ;-) due to the stone sinking and leaving an air "hole" in the water in its trail; this is then filled gradually with water which makes the sound raise in pitch; a bubbling sound due to air bubbles trapped under water by the stone, emerging. read more