Sometime in the last week or three something odd has happened in my mother's house. There's a downstairs utility room which has a WC in it; when it's flushed there a second or two of silence then an increasingly loud humming or moaning sound - which mum tells me is audible also in the room next door and the one next to that (a kitchen). The sound continues for 20-25 seconds then dies away.
The WC cistern is inside a sort of cupboard, which I opened last time I was there. There's no sign of any water leaks (mum's biggest concern). When the WC is flushed the copper pipe which brings water to the cistern is definitely vibrating. If I grip the pipe the vibration and sound both reduce. The CW comes from an attic CW tank which must be about 20 feet higher.
I assume the noise is audible elsewhere because it's being carried along the CW pipe to the kitchen...
But why would something like this suddenly start?
The cistern's float and the valve it operates seem to be working fine, though the valve is a but grungy on the outside. I did wonder if it might have something adrift inside causing turbulence in the water flow, and in turn whether that could cause a problem in the supply pipe?