I'd bet money It's your wdh bars(if you have the type that lock up into the receiver), squirt a little WD-40 on them and the ball. If you have sway control, maybe it's way overtight, don't lube that! I was told to just tighten it until the stud attached to the handle is flush with the nut on the back. It's totally normal for those setups to make a little noise, especially on tight turns.
I always loosen my sway control before going into a campground. Once you cure the squeak with WD-40, you can decide if you want to, 1- use that every trip, 2-let it squeal, or 3-grease it with automotive grease and have it all over your pant legs for the rest of your life.
I use WD-40 exclusively, it will easily last a trip and I just reapply before the next one.
I'm not talented enough to slop grease all over everything and not get it on myself. I have tossed two pair of shorts from rubbing up against a greased hitch.