Iain,
Keith is spot on, before I owned a Van with the Alko Hitch I used a Bulldog 2000 Q. This always Creaked, Sometimes after only a Few Miles, However I noticed that when it was Raining there was no Noise. So my crude remedy was after Hitching up, pour some Water over the Pads, over the years this has caused some ammusement from the People Watchers, but on one Trip from Home in the Midlands it was Silent all the way to the South of France. Another way of "Watering" the Bar was on the Last Night before Returning Home I put the Stabilizer In The Fire Bucket! This would then last all the way Home.
The purists will tell you that the Noise is caused by accumulated Dust between the Friction Pads becoming Polished by the Turning Action, and to send the Bar away for service. However as this noise was present from almost Day 1.And as Keith Said, if the bar is in Good Condition, I fail to see how this would cure it. Incidentally I have told many people about my Water cure and even wrote to several Mag's but I think the Cure appears too simple to be believed.
Regards Eddie1 From Nottingham