Hmm!
The noise can be many things of course, water hammer can also show itself in many ways. So once again its guessing time.
First off! Has the noise just started? If so what has changed? new taps? water company increased mains pressure? loose pipes? and so on.
What causes water hammer is explained by good old Mr Newton and that is for every action there is an equal reaction.
So if you stop a stream of water suddenly instead of gradually slowing it down you get a backward force equal to the forward. And so it makes the pipes bang.
In the past, local water authorities insisted on screw down valves being used on their water mains as stop cocks for this very reason.
In other words unlike a quarter turn plug cock they never suddenly shut the water off causing water hammer back pressure.
Today however we have ball o flow valves, which are really fancy plug cocks at the inlet point of every appliance that is fed off the main.
The thing is they are not used very often except for servicing or repair, so its thought the problem isn't so great.
But we also have lever arm quarter turn ceramic disc taps that work exactly like a plug cock, so obviously if you have just fitted a pair of these, have a look if they are causing problems elsewhere. They are usually popular with older people if they have arthritis or anybody who just prefers an easy tap to turn on and off. I personally like them.
What also a hum, which doesn't sound anything like a bang, can be, is due to the same thing.
In a cistern the speed and force of water causes minute waves on the top of the water, which makes the ball float valve open and close very rapidly which can make humming noises that is why Feltham suggested changing the washers as a first cheapest step.
Even worn washers and worn stop tap spindles can do the same. Not to mention loose pipes
There are loads of things that can make a pipe hum and also a variety of things you can do about it.
And if you can find out exactly where it seems to be coming from, then perhaps people can help a bit better with possibly a little bit more knowledge about your system.
But I would say try the cheapest things first, it would do no harm changing the ball valve washer, as they are only about 10p each or should be.
