On Tue, 13 Jul 2010 11:05:21 +0100, Bob Minchin
wrote:

The hammer will be coming from the fill valve. I expect pressing the
flush gently start the refill slowly rather than quickly when doing a
'fast' flush.
Maybe changing the diaphragm in the valve will shut it up.

Looking at the top picture at
http://www.littletyke.myzen.co.uk/cistern/index.html do you mean the
white component in the right corner (closest to tiles) on which the
ball valve arm is mounted? It has a cap of some kind with "teeth"
around the circumference. Presumably this can be unscrewed?

Or fit a hammer suppressor in the pipe nearby.

I could, but this hammering only started fairly recently, so something
must have happened to cause it, e.g. something or other worn after
five years' usage.

MM