Search the websites. there is loads of stuff about this.
essentially, the flap valve (this is the bottom rubber washer...typically abou 1 1/2 in diameter..grey colour) is leqking into the bowl. when the water in cistern is sufficiently reduced, it will re-fill (its this that you are hearing, not flushing (scary if you're home alone).
TURN OFF THE WATER
Take off the cistern cover by lifting up the flush buttons and unscrew with a cross-head screwdriver. Twist the whole assembly anti-clockwise and lift it out. Replace the washer (this is removed by prising off the bottom plastic fixing washer). A short-term fix is to get a nail brush and give it all a good clean or even to turn the washer over.
My experience is that this will never be fully resolved. suggest you get a supply of washers !
i have also read that this can also be resolved by replacing the flushing mechanism...the name Geberit is mentioned. You will first have to make absolutely certain it will all fit.
by the way, there is another possible proble...it might be that the moon shaped rods on the flushing buttons have been incorrectly cut and so will continue to leave the flush mechanism on.
Frank
June 2009
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix toilets.