The copper pipes in your house can bang and rattle for various reasons. They can make a moaning or whining noise that sounds like singing because of certain conditions, which occur when air gets trapped inside the pipes somewhere along the line.
You may think your water lines are air tight but sometimes leaks develop. This is common when the washers in the valves become loose, damaged or worn. The air getting sucked through the tiny gaps into the lines, with the force of the moving water, acts like air blown through a wind instrument.
Whining pipes can make people nervous because they make an eerie, haunting sound. It is difficult for a lay person to track an air leak. A professional plumber must bleed the pipes and use pressure testing equipment to locate and repair the leaks.