Tow Hitch Groan

We had our Pegaus caravan serviced two weeks ago and mentioned that we were getting some groaning at low speed from the hitch.

On picking it up they confirmed that they had cleaned the Alco pads and it should be ok now! And it was at first! But by the time we arrived at our site there was a small amount of groaning again.

As it happened we had to have the mobile engineer out last week and mentioned this to him, he chacked the pads and said these were fine and also had a look at our tow ball which he said was ok too but would give it a clean to be sure.

On leaving the site the groaning was awful and didn't improve much before we left it at our storage site.

Any idea what else we can do? Anyone else had this issue?