Banging pipes

[Nige62]

A mate of ours has got a problem with the cold water pipe banging in the loft when turning off the tap/shower or the cistern stops filling. I was talking to a guy who used to be a plumber and he reckons its caused by very high water pressure and if left could cause damage in the long run. Also the only way to cure this is to fit some special valve/restrictor (I cant remember exactly what he called it) in the supply pipe and that simply turning down the mains tap will not help.
I was thinking that this sounded more like air trapped in the pipes but he says no.
Any ideas if he is right or not, and if he is what exactly is this valve thing, and where should it be fitted.
Thanks everyone

 

[holty]

called a shock arrestor. but pipe clips are prob cheaper option first

 

[Nige62]

Thanks for the quick reply.
All pipes were fixed down when new combi was fitted so it sounds like the second option.
Where exactly should this part be fitted, by the supply tap or in the pipes in the loft where the banging is? hopefully not the supply as thanks to the kitchen fitters there is no access to this anymore (apart from turning on/off)

 

[holty]

just because all your pipes were clipped doesnt mean there not touching. also try opening the mains stop tap fully open.