Hi, I' have been caravaning for just over 12 months and done a few tows with the outfit.
We have retractable tw bar which initially we had problems. The car dealer replaced it under warranty and on the first tow with the new tow bar was ok, however we have just come away for our summer break and whilst towing this time there is a clunking sound (as though the ball is too small for the clamp). I have taken the carving a main dealer last week and asked them to checkck the tow bar and confirmed ok. I have also called out an Caravan Engineer who checked the towing mechanism and also confirmed ok.
Our Sorento has a Witter removable towbar, there is the odd clunk when towing. Like you we had car and van checked-all okay. It does not happen often.
There could be a tiny bit of movement in the removable part, as ours slots in then locks, but I cannot feel anything moving it by hand.
The van hitch can rotate slightly about its axis, maybe its that?
The Al-Ko stabilizer hitch has friction pads, which wear, the handbook tells you how to check them.
------------- DS-There's more to life than football!!!