Knocking pipes

We have moved into a newly built duplux and are getting knocking sounds when we run our hot water tap. It seem to knock louder when the water is hotter. We had a look but couldnt get acess to pipes as they run up the lenght of the wall. Any ideas of what it might be would be really appreciated.

Hi I had the very same problem when I moved into my house.If its a brand new house in a housing estate saw it to the plummer and he should fix it.If you can't get the plummer its most likely the mains water pipe in your hotpress is just a little bit loose and needs to be fixed tightly to the wall.Thats what the plummer did to mine and the knocking hasn't come back.