Knocking Cold Water Pipe

[AudioDave]

Hi all.

I'm trying to find the source of my knocking cold water pipes. It only seems to happen when nothing is in use.
I have a new mini arrestor on the washing machine. I've bled all the radiators. Switched off the main (bore) valve and opened all the taps to drain the water, then slowly opened the valve etc. I've also reduced the flow to the toilet cistern, which seems to drip from the inlet. Photo attached, excuse the state of it. It's enclosed and difficult to access fully.
The knocking is mainly in the kitchen pipes. Sometimes knocks 3 times with 20 second between each knock, then nothing for a few minutes, then repeats.

Pressure into the house from mains is 3 bar.

Any help is greatly appreciated with virtual beers.

 

[MeldrewsMate]

... It only seems to happen when nothing is in use.
...Switched off the main (bore) valve and opened all the taps etc and reduced the flow to the toilet cistern...
...The knocking is mainly in the kitchen pipes. Sometimes knocks 3 times with 20 second intervals, sometimes randomly.

Please re-read and re-write your post.
It makes little sense. Make it easier for us to correctly interpret the conditions.
Is the main (bore) valve still off?
Are the taps still open?
Is it 3 knocks, 20 second pause, 3 knocks, and repeat?

 

[AudioDave]

Edited now, MeldrewsMate. Been up since 02.30 for work, the brain isn't functioning fully.

 

[Scally-Ho]

Do you have a cold-water storage cistern in your roof space?

 

[AudioDave]

No, the old one was disconnected/dry. The cold water pipe used to run through the attic and to the bathroom, but we had them redirected through the kitchen (for the bathroom).