Clunking noise while towing

I have a Reese 18K signature slider that had a clunk. I checked out all the bolts and adjusted the donut anchor levers so that they were tight and the clunk continued. I finally determined that the right side dog that holds the hitch in place on the slider was somehow lifting causing the right side to pivot and cause the noise. I installed a bolt with a locking nut in the hole above the right side dog that holds the hitch forward and that cured the clunking noise. The locking pin above the hook on the left for some reason did not keep both sides of the slider locked down. It took me a few years to figure out what was going on. The hitch is great now that is completely tight.