A: This is caused by unequal pressures, usually by the cold being much higher than the hot.
You will notice that by changing the temperature the noise will change and go away, as the temperature in the cold water mains changes this will also cause it to go away.
Fitting a pressure reducing valve to the supply will solve this problem also if the existing temperature cartridge is worn fitting a new cartridge may solve the problem.
Answered 283 days ago | The doc