Plumbing Question

What you are describing is most likey 'water hammer'. The noise is caused from a shockwave created typically when a valve is quickly open or shut.

Beyond being noisy, water hammer (a hydraulic shock) can cause significant damage.

Devices are marketed that can be added to systems to arrest water hammer. Also, slowly throttling valves open or closed is a work around.

Water hammer happens in hot or cold water, but you may be hearing additional sounds in hot water as created areas of low pressure cause hot water to flash to steam and then again collapse making a popping sound similar to cavitation.

Pipes under pressure deflects along lengths on bends/elbow due to unbalance forces created by the pressure and bends. You can imagine if the pipe are fire hoses, these pipes will be straighten due to pressure. Mere releasing the pressure by opening the faucet will have a reaction forces equal to the force created by pressure in an opposite direction. This cause the sound you usually hear "banging".

In commercial installation and standard design, this is eliminated by usually employing your pipe lines with air capped chambers and water hammer arrester to damp the impact.

The water hammer effect there for the "banging" noise is actually experienced when closing the faucet, not at opening.

If you hear a SINGLE bang when opening or closing the faucet, this is caused by a poorly supported pipe. The sudden change in pressure causes the pipe to jump and bang into a joist or stud. IF you can find the location where this occurs, you can usually fix it with a 50 cent pipe support.

If you get a prolonged or continuous "machine gun" rattling round when the faucet it opened, you have a TRUE water hammer problem. You can purchase and install water hammer arrestors, but this is a job for an advanced home-plumber or a professional plumber.

If you hear ticking sounds for several minutes after opening or closing a faucet, this is caused by thermal expansion/contraction. It means the pipes are clamped TOO TIGHTLY to joists or studs. The thermal expansion/contraction changes the pipe length slightly and the pipes have to slide through the overly tight clamps making the tick--tick--tick sound.

Best wishes.

This is referred to as hammering. Typically caused by cold water replacing the demand for hot water being pulled from the hot water tank. If you turn on the cold water it is bypassing the the tank where as the pressure of cold water entering the water tank to maintain a hot water level creates the hammering.

Some possibilities:

• It might be because the pipes are inadequately restrained from moving. According to Newton's Laws of Motion, when a body (the fluid in the pipe) undergoes an action (starts to flow and changes direction at bends) there is an equal and opposite reaction (the inadequately-restrained pipe moves, clatters against something and makes a noise).
• It might also be because there are bubbles in it and the bubbles cause flow fluctuations at restrictions like taps (especially if the water is close to or above its normal boiling temperature for the pressure in the pipe).
• It might also be that the flow is happening at a Reynolds Number greatly exceeding 2300, and the resulting turbulence is impinging on surface phenomena on the inside walls of the pipe, and the vibration is causing sound waves to issue.