Diesel Groan
I am relatively new to caravanning and towing, 4 years to be exact. Last year I started to hear this awful screeching groaning sound while towing, most pronounced at slow speeds when turning or reversing. I thought at first that the mounts for the ttowbar
frame under the rear of the car were coming loose. After searching the internet and Alko website I found on the Alko site under maintenance a refrence to DIESEL GROAN. Deposits from diesel exhaust being the culprit. It is no good polishing your ball to
keep it clean as the problem is aqctually deposits on the friction pads which drag on the ball and cause the noise. Solution is to pop the pads out every 6 months and polish the dished surface with a fine emery cloth or sand paper. The deposits are obvious
once you can see the face of the pad. Incidentally I have mentioned this to several people who have towed with diesel cars for many years and have never heard of it.