Knocking noise from PVR

[helpneeded]

Knocking sound coming from PVR.

Have an in-line pressure tank set at 3.5bar, but downstream a 3 bar PVR. The PVR seems to knock at random times for hours and hours, which is driving me crazy. Is the inline pressure tank pressure set to high?

 

[king of pipes]

Can you post some pictures please …??

 

[helpneeded]

Can you post some pictures please …??

Sure, please see above. The noise is definitely coming from the pressure release value - as if it is continually opening and closing for hours and hours. If I turn the water off to the pvr, then all sound stops. I am thinking there is too much pressure in the pressure tank as it says it’s at 3.5 bar / plumber wrote set at 50psi on it, but then fitted a 3 bar pvr. Any help would be appreciated as the sounds is starting to drive me crazy thank you.