Hi, For the past 3 weeks I've noticed a sort of hissing noise from the water pipes all over the house (not central heating). Its the sort of noise you get if a tap is half turned on - hissing isnt the right word. Bascially it sounds very much like water is running through the pipes. The pipes run from behind the washing machine in the kitchen (great place for a stopcock), up the kitchen wall beside the combi bolier, along the landing to the bathroom. I can hear the noise from behind the washing machine, around the boiler, along the landing, in the bathroom, basically anywhere there is a pipe. I've tried switching off the taps to the washing machine thinking a recently installed new washer was the cause, but it makes no difference. I can find one leaks or evidence of leaks throughout the system. What on earth is causing this noise?