When the cistern starts to fill at the final stage their is a loud bang. The make of the toilet is armitage shanks.

mthomas, September 2009

As the water finally shuts off, there is a pulse of pressure sent down the water pipe....so, the banging could be a pipe that isn't clipped down to the woodwork, or maybe its the filling valve itself. If you have a Torbeck valve fitted instead of the existing one, you'll get a quiet fill and much less chance of any other noise.

John, September 2009