Could anyone advise me on a problem i may or may not have with my Knott coupling fitted to a 2023 Eriba Touring 540. After pulling up at a junction and then moving off, there is a clunk coming from the coupling as the free play is taken up, i assumed rightly or wrongly that this action should be dampened in some way for a much smoother take up in the coupling. Having owned 3 vans prior to this iv never had this problem before although they were Alco couplings. The van is stil under warranty and i intend to contact the dealer but would appreciate your thoughts as to be for-warned . Thankyou.

sounds like the overrun damper has failed

It does sound like damper failure but that usually occurs on much older vans. The test is to see if you can push the hitch in easily by hand. If there's significant resistance the damper is ok. A poorly damper usually causes a clonk as you brake as well.

Some other random thoughts:

Loose towbar securing bolts
Hitch grease needs replenishing (does hitch head wobble when 'shaken')
Hitch head securing bolts, if any, have loosened.

Usually when the damper has failed the Eriba brakes will start to dramatically snatch when you brake in the car, as I found out with my old Puck