Sounds like it might be either air in the pipework feeding the WC cistern or vibration in the inlet valve to the cistern. If there is a local isolator valve for the water feed to the WC, you could try turning this down slightly. If not try adjusting your mains water stop cock (usually near the kitchen sink).
DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!