One of my toilet cisterns makes enough racket to wake the dead
(certainly wakes SWMBO if I flush at night anyway). It's a ball valve
type, and we have mains-pressure water throughout the house. When the
cistern finishes refilling after flushing, as the valve closes off
there is an almighty, well, thunk sound, which reverberates around
the house.

Changing the valve to a Torbeck one is on my to-do list, but without
knowing the cause, will that definitely cure the symptoms? We have
two other loos in the house, one Torbeck and one ball valve, neither
of which have a problem.

Thanks
David