When the toilet is flushed a noise like a foghorn begins and the cold water tap vibrates in the bathroom. Running the tap seems to help the noise to come to an end quicker

Fed up Housewife, January 2013

The quiet ones are called Torbeck valves. they might look flimsey but I've been using them for 30 years.
They come in 2 variations Bottom Fill and Side fill and both eliminate cistern fill noise caused by mains pressure screem.
Google 'Torbeck Valve' every body sells them
Should cost you about a tenner

GB in Wales, January 2013

change the toilet filing valve. u can get silent filling ones. its most likely worn and when they get to this stage they become noisy.

kash, January 2013