In a nutshell there is a very loud vibration noise coming from one of the header tank pipes (exiting the tank). The pipe is physically shaking and I can feel it in my hand.
From what I have read I thought it might be water hammer, however yesterday it went on non-stop for over 15 minutes - so not so sure.
I realise it is going to be very hard to diagnose but I have uploaded a video which hopefully somebody might be able to have some ideas on...
Many thanks!
https://www.youtube.com/watch?v=zCRYXQ3Dx18
