I have a loud droning noise and vibration on the cold water system to the bathroom. It stops completely if you flush the toilet but once the cistern fills back up it starts again. Turning the cold tap on the basin on to a dribble can stop it for a while but that doesnt last for long. The ball valve in the cold tank has been changed after the overflow from the cold water tank had been running constantly and since then this problem has arisen.
If its the valve on the cold tank that's making the noise then try reducing the water pressure.
I had a problem whereby if I opened the main stop valve for the house fully it caused a racket in the cold tank when it was filling. Turning down the valve a little stopped the noise. It was only turned down enough to stop the noise but not enough to make a noticeable difference in filling time for the tank.