There are gurgling or banging noises coming from pipework. This usually comes from pipes between the boiler and tank and often happens when the boiler starts up.
Air has become trapped in the pipes and is being forced around, causing the pipes to vibrate and, in some cases, bumping the pipes against the woodwork in the floor.
Air does not belong in this sealed system of pipes but it can get in when the system is first filled or, if there is a leaking joint in the pipework, air can be getting in as the water drips out. The latter situation is, of course, serious, but very rare.
What you can do
This is best left to a qualified plumber because it can be quite difficult to solve, especially because it is inconsistent.