toilet cistern makes a noise/water running from outside pipe?

An irritating but not major problem which is puzzling.The upstairs toilet cistern (or pipe leading to cistern) makes a spasmodic gushing sound (similar sound to flushing or tap running hard) for about five seconds only. This happens once or twice a night, sometimes more. Can also happen in daytime. Is it possibly cistern automatically refilling as I've noticed a minute amount of water seeps into the pan from above almost constantly? Is there a solution?

Tom
September 2009

Adjust the valve on the pipe that goes into the cistern at the back/underneath (usually on the right hand side) with a coin or flathead screwdriver so that the line points vertically up (i.e. is fully open). This should get rid of the hissing/whistling.

Jasb@h
November 2007

Adjust the valve on the pipe that goes into the cistern at the back/underneath (usually on the right hand side) with a coin or flathead screwdriver so that the line points vertically up (i.e. is fully open). This should get rid of the hissing/whistling.

Jasb@h
November 2007

new valve / or a repair kit. both easy jobs. the rubber has gone hard inside the valve.

hi-spec plumbing
January 2007