On Jul 13, 9:37 pm, MM wrote:
My low-level cistern has a button to press to flush the loo. If I
simply press the button I get water hammer noise.

If the mains water pressure has increased recently that could cause a
problem. I have fitted a pressure reducng valve in my main pipe and
that has fixed all my plumbing problems.
Rubber diaphrams can cause hammer while fibre diaphrams won't.