PRV Multibloc Valve Strange Noise

[Leaky Blinder]

Having a problem with a recent installation. Fitted new unvented cylinder and boiler. Everything fine for 6 months Then I get a call from my customer reporting a water hammer issue. I attend site and fit a shock arrestor. 2 days later he phones me back... still doing it. He says when you open a tap you get a pulsing sound. Like water hammer that that has a bouncing sound. I attend site again and find that the cold main is a little under supported and where it passes between the shelves it's banging against the wooden batton. This time I'm dead sure I've sussed it. I added some clips and even a small piece of lagging around where it passes through the shelf for good measure..... 2 days pass......phone rings!! Making the noise again. This time he sends a video along as well which I will post here if possible. I am at a loss as I haven't experienced this before (10 years in the trade).
If anyone knows or has seen this I would appreciate the help.
Thanks in advance!
Matt

Edit: I have since clipped the expansion vessel hose so it doesn't flap around like a wild gibbon. We've all done it

 

[SimonG]

Hard pipe the expansion vessel.

 

[Leaky Blinder]

Hard pipe the expansion vessel.

Hmm not a bad idea actually I might give that a go. Iv'e tried moving the expansion vessel connection from the side of the multibloc to further down near the cylinder and still same issue

 

[king of pipes]

Agree with Simon hard pipe the expansion vessel fit a flow through valve we should all be fitting them as standard in my opinion , make sure your expansion vessel pressure is set 0.2 bar below your incoming pressure . Kop

 

[Leaky Blinder]

Bump! Still having the same issue. I have returned to site before Christmas. Changed the prv for new and hard piped the exp. Said it was fine for a couple weeks and then the noise returns.
At this point I have no idea what to do. Weirdest issue I've ever had.

 

[Chuck]

The hairpin bend a few inches from the multibloc looks a bit sinister to me. Maybe that's provoking the hammer?