Fitted a new pair of kitchen sink taps for my mother-in-law a few weeks
back. The hot one is fine.
If you turn the cold one on maybe half a turn to a turn, it makes an awful
banging noise and the water flow pulses a couple of times a second. If you
keep turning it on, it stops this and flows freely.
I'm satisfied this isn't an airlock or anything. In fact, if I press down
hard on the head of the tap as I turn it, it's fine. Ditto, if its left in
the posiiton where the noise occurs, turning on another cold tap elsewhere
in the house stops it too.
Thinking maybe the mains pressure is a bit high, I've tried turning the
stop-cock down a bit, but to get the banging to stop that way means I have
to almost turn it off and the pressure is then a bit too low.
My conclusion is the tap valve must be a bit iffy even though its a
reasonably good make (Pegler), causing it to bounce with the pressure.