Repeated "water hammer" in pipe

A friend of mine asked me if I knew why one particular tap in his house "vibrates" if the tap is turned about half way to a certain position.

I don't know if this phenomenon has a particular name, (seems common enough), but it is when a tap is turned on about half way and the pipes in the way start to vibrate (bang-bang-bang) repeatedly, kinda like a repeated water hammer. Turn the tap a little more and it goes away.

This got me thinking. I assume it has something to do with the flow of the water creating some kind of resonant frequency in the pipe which causes it to start to vibrate?

What is required to fix the problem? I assume if it is a vibration problem that a few more clamps on the pipe would be the simple solution. (The offending pipe is in an upstairs bathroom and so difficult to access).

Thanks.

Start with a new tap washer and see what happens. An old or worn or even a certain make of washer will sometimes 'jump' up and down on the seat causing hammer.

Thanks wonderplumb..... He will give it a try.