A strange occurrence at home over the last couple of weeks - at random
intervals, usually, but not exclusively, at night, I can hear water
running for about five seconds. Don't get much chance to investigate
in five seconds! It sounds as though: valve opens, water runs (in
pipe), valve closes, silence.It's almost as if it's a wc on half flush
but with slightly more pressure and none of the associated dribbling
at the end. I've checked the header tanks in the roof and my wcs but
have found no signs of any activity that might cause it. It has
happened twice in 30 minutes but the intervals are usually longer. I
hear it better upstairs than downstairs but that might be because my
shower room has the main cold water inlet pipe running through it
(from below) and I'm further away from that when downstairs.

Any ideas anyone? Where's the water going? Have I become haunted?
TIA