3-Way Cascade Tap Leak

[Ben9790]

Hi All,

I have installed a cascade 3 way tap and a water filter kit, links below.

When running the hot and cold water with the water filter valve closed - all fine, no leaks
When I first open the valve to the water filter supply and run the filtered water part of the tap - all fine, no leaks.
Now that the water filter valve is open, when I run the hot and cold it starts to leak from what looks like the connection from the water filter to the tap.

Baffed.

Any ideas?

Also, the tap screams, any idea on what needs replacing (and where it is if you've installed one before) to stop the noise?
It screams in the mid-range. Turn it on slightly or full blast and no noise.

Tap: Cascade 3-Way Tap Chrome | Fountain Softeners - https://www.fountainsofteners.co.uk/cascade-3-way-kitchen-tap-c2x11547057
Water filter kit: BWT Water Filter Kit - https://www.NoLinkingToThis/p/bwt-water-filter-kit/14306?_requestid=96650

Thanks
Ben