constant running/dripping water in or near hw tank

[ewo01]

Near to or in the hot water tank there is a constant flow (or that's what it sounds like) of water. It's only a slow sounding flow but it is really getting on my nerves! When the HW is on (not the CH) it is making this noise. It happens whether there is a tap on or not and the only way to stop it is to turn the HW off. Is this normal?? And if not, how can I stop this dripping/flowing annoyance??

 

[sterose]

Is it a dripping sound or a 'flowing' sound?
Does it go away instantly when you turn HW off or only gradually.

I would think it might be the ball valve (they drip for a while, even after the tank is full).

 

[ewo01]

it is a flowing noise, although not a smooth flow (difficult to describe). The sound does stop as soon as I turn the HW off.

 

[oilman]

Sounds like it is air in the pipework going to the heating coil in the tank. Is there an air bleed point connected to the top of the coil?