noisy cold water mains - advice please

I\\\'m considering buying a house which has quite a noisy water sound all the time. It can be heard in the kitchen and the lounge coming from in the wall - most probably near where both these rooms meet in the middle of the house. The noise is there all the time and is sort of a whooshy noisy which sounds like water permanently running through it, yet no taps are on, no leaks visible anywhere, nothing using the water, and yet the noise is always there.

The owner got a plumber round who said it was a noisy mains.

But I don\\\'t want to buy the house without knowing that this sound can be fixed and eradicated. I\\\'m hoping someone has some suggestions as to what it could be. Any estimate on cost to fix would be helpful if one can be made.

Any help would be greatly appreciated, as I like the house but can't go ahead unless this noise can be cured.

For there to be a noise, water must be flowing, and may indicate a leak somewhere. Do you have a water meter which you can use to see if there's a leak with allyour taps turned off.

I don't believe the house has a water meter.

It seems that it must be a pipe that runs vertically from the ground to the upstairs/loft area. I wonder if the cold water header tank could be filling permanently, but I would expect this to result in water coming out of overflow pipe on the back of the house somewhere. I didn't see any water coming out, nor the outside tap leaking water. Do all cold water header tanks overflow directly to the exterior of the house?

Thanks for any help

Turn the main stop cock off in the street and see if it stops.