Check the feed pipe to your ballcock there my be a line valve fitted, this valve is there to turn off the water supply if you need to work on the toilet, you can also adjust the water flow with it as well, turn the valve with a flat blade screw driver a little to the left or right to speed up or slow down the water supply, if your lucky this will quiten the noise. Good luck.
Freddy Fix it.
March 2006