Pipes are almost alive -- they make warning sounds when something is wrong, and squealing is one of the more distressing sounds they can make, second perhaps only to banging. The sound usually occurs because pressurized water is passing through a restricting aperture. It could mean sediment or air is stuck somewhere in the pipes or that your pipes are getting old and need to be replaced.
The Galvanized Pipe Syndrome
If your house predates the mid-20th century, the water pipes may be made of galvanized steel, which was in common use before being replaced by copper. Galvanized pipes corrode on the inside, and as the corrosion gradually builds up and restricts water flow, you usually notice a loss of pressure at faucets. This pressure loss may be accompanied by squealing at places in the pipes where the corrosion is heaviest. It's more prevalent in hot water pipes for two reasons:
- Hot water accelerates the formation of corrosion
- Hot water is under greater pressure than cold water.
Replace your galvanized pipes with copper, CPVC or PEX ones.
Debris in the Pipe
You may have just completed a plumbing repair that involved modification of the pipes, and in the process, some debris may have become lodged in an elbow or a valve and is restricting water flow.
Flush the pipes. Remove all the aerators from your sink faucets; open the hot and cold water valves on all the faucets -- including in tubs and showers -- and let the water run for about a minute. Flush all the toilets in the house while the water is running, and open the water dispenser in the refrigerator, if there is one.
Air in the Pipes
If air gets into your water pipes, it tends to collect at the highest point in the pipes and form a bubble that can restrict water flow as effectively as solid debris. If you allow this condition to persist, an airlock may form and cut off the water altogether.
Bleed the pipes. Like flushing the pipes, this procedure begins with turning on all the faucets and taps -- including the water dispenser in your refrigerator -- and flushing all the toilets. You should notice the water spurting at some of the faucets as air escapes. When all the spurting has stopped, begin systematically turning off the faucets, starting with those on the top floor farthest from the water supply.