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 I press it initially very gently, so as to release some water into the bowl, and then press fully down, I DON'T get water hammer.
So where is the *actual* water hammer noise emanating from? I've read before that water hammer is something to do with high pressure and valves, but I don't get how this only started recently (over the past couple of months).
This is the cistern internal 'gubbins':